Mine would probably have to be the thought of having surgery. The idea of being cut open and having my insides sewn and shifted while I'm asleep... just makes me... want to...

I absolutely despise bees, wasps, and hornets. I scream and run the opposite direction when one approaches. I've been told millions of times that running away will make them more wont to sting me, and the "they won't harm you unless you harm them" garbage, as well as the "they don't even sting" drivel, but I don't care. They still scare me to death. I've only been stung by a bee once, and it was at the beach a few years back and underwater. I have been chased by too many as a kid to ever be fine with them, and I'm okay with that now. Except for March, where they're hovering around my front door and making me fine with staying inside, except for not being able to freely run around in the yard with my dog. I never saw that fear as 'irrational,' per se, but I know other people who see my reaction to it consider it irrational. I can't fathom how people can be fine around bees. I just can't.
I also have a deep aversion (though I guess it'll go into 'fear') to calling people or receiving phone calls, even from people I know fairly well. I let most phone calls go to voicemail as a result and either text back or ignore the call indefinitely as a result. I can only call family with no issues, and very, very, very close friends. Other than that, even if it's to call a place and ask what services they offer or if something's in stock or to set an appointment, I get scared and try to make someone else do it for me. The only consistent exception is if it's work-related. I don't mind that for some reason--in terms of actually overthinking it and becoming afraid. I dislike calling people in general, but I am more okay with it if it's for work. At times, especially if I'm alone (for some reason this is exacerbated around other people), I'll just buck up and do it. I also work in a callcenter-type deal right now, so I receive calls at random and besides the whole drag of it being work, I just deal with it.
By extension, I also have a fear of small talk, though I can pull it off if necessary. I'd just really, really, really, really prefer not to. I either like to talk about everything and be comfortable or just not talk at all.
And yeah. Other than that, I've been known to have trouble sleeping because I keep thinking about the probability of someone breaking into my house or a family member's house, or the house burning down, or one of my pets dying or running away. I can usually talk myself out of those sorts of fears, though.
I'm afraid of American's. I'm afraid of the world.
I'd rather risk something going wrong after being cut open than know something will go wrong if I don't.
I am deathly afraid of slugs, worms and other worm-like creatures. I'll have a minor panic attack if I encounter one of those. Not fun.
You know those salt circles you see on TV when people want to keep demons and ghosts from their haunted houses? That's what I'd like to do.
Good response on multiple levels. David Bowie/Trent Reznor and all.
I had two knee surgeries as a kid (at age 10 and again at age 11) and thought it was so fun and trippy. I was more excited than anything, being a naive kid and knowing my legs would be straightened and I'd miss school for the first time in my life (my parents were insanely strict on attendance--even if we were sick and vomiting, we had to show up to school and then ask to leave early so we'd be marked present). I thought the feeling of being so drowsy right before the surgery and then waking up and being so out of it that you don't know if the surgery happened or not so trippy.
I think nowadays I'd have a lot more trepidation, like you, when thinking of knives cutting into my skin and also the stories you hear of people waking up in the middle of surgery, completely paralyzed and unable to alert medical staff. I was told to set another appointment with an orthopedist at some point to see about getting my last set of staples removed, but I'm thinking to myself that I think I'm juuuust fine, haha. That and I don't want to wait several months to be able to kneel down and work out and such.
Why not something like this? http://3.bp.blogspot.com/-V_60yoBMoxY/T_D6YLOsFBI/AAAAAAAAAMI/kmyndP5uD1U/s400/hi-slug-wanna-play-a-game-saw-240x180.jpg
Surgery isnt that bad, I had severe appendicitis when I was 13 and my appendix actually popped like a balloon. I woke up 2.5 months later (I was placed in a medical coma to keep me under control as my primal side came out and I was ripping IV's and tubes out and it took 4 orderlies to hold me to the table) and hade 3 new cars on my stomach. 2 in the side and one just above my naval. The pulled a tube that went into my chest near my collar bone and I also have a scar there too. Stuff like that doesnt bother me.
I'm actually hard pressed to think of something that I am completely bonkers afraid of.
I'm not sure if it's a fear, but I get really nervous and uncomfortable when I'm talking to people I don't know. I stutter, I tend to ramble and feel extreamly self conscious.
I don't think that's necessarily irrational either.
But then I'd have to stay in the presence of one, and that's never going to happen. While it looks like an appropriate fate for such an abomination, sadly I'm not much of a sadistic person.
I was just thinking that it's irrational because there's no real repercussions to sounding like an idiot, but I get your point. Also doesn't help when the people I'm around on a regular basis tend to have no trouble interacting with people they don't know well.
The people around me usually just try to be my life coach and tell me I just need to "get out there" more and I'll get it. Socialization makes me exhausted so I don't feel much of an incentive to have a huge group of friends. But it makes moving to a new area hard, haha. Luckily my best friend is just like me in that department so we bond on shared social flubbing.
Heights and my health, the latter one coming from an anxiety attack I had a little less than a year ago. Its improved slightly, but I still sometimes think "maybe I need to get checked for cancer, or diabetes." Doesn't make any sense but I have this fear that I'm gonna get really sick and die, or have a heart attack... and I'm 19.
Spiders.
It is thought that the widespread, often irrational fear of spiders is an evolutionary remnant behaviour.
I could do without it though. A tiny spider, does nothing. But even a quite small bigger spider, the ones where they are big enough for you to see the eyes and hair on the legs, they instill a sort of primordial revulsion and fear in me. I can not be in the same room with one until it is dead. A feat usually achieved by throwing a large book at it from quite a way away.
It is a completely irrational fear, where I live it is too cold for dangerous spiders to occur and the biggest ones we get are cave spiders, the ones that moved from the caves into houses with us.
Mind, they can live to be thirty and never stop growing so they can end up bigger than your hand. The old ones almost never show themselves to people though, they got old cause they're wily.
But even these are of no danger to people. Still, hairs stand on end not just on the back of my neck but over my entire body and I am gripped with a panic, it is undescribable.
All the while knowing they are harmless.
Because of my fear of spiders I have become quite fascinated with them and have studied up on them every opportunity.
There are some really amazing spiders out there in the world, spiders that use a strand of web to lassoo prey with, spiders that build their nest under water, solitary hunting spiders with a brain the size of a grain of sand who exhibit complex hunting behaviour you'd normally expect from a tiger or wolf.
Fascinating creatures really, I just don't want to see them in my house. Or in a zoo or pet store. I get the heebee jeebies even from television and pictures in books, but I dont let that stop me.
If you give in to fears like this you are re-enforcing neural pathways and in effect making your phobia worse. The worst thing anyone with any phobia can do is to totally and completely avoid all triggers of said phobia. (Which is why I was always really opposed to those 'no spiders please' requests before Skyrim was released.)
I'm not afraid of heights, just hitting the ground.