Personally, one thing I can't take seriously is when an ugly person tries to pick on a pretty person. It just seems like jealousy to me.
Now, I know that sounds pretty weird labeling ugly and pretty, but to me, if someone who looks stereotypically dorky/ugly/weird/creepy tries picking on someone who is stereotypically popular/cool/pretty I just can't take it seriously and just consider it as the ugly person being jealous.
It happens all the time, amongst my friends even. One not-as-attractive girl will start talking crap about another kind-of-hot girl out of no where about how "her hair is SO fried" or "she looks stupid in florals" and "she's such a wannabe" and I just think "you're just jealous because she looks good.". I have a philosophy saying that a pretty person will always be pretty and will forever be treated as such in comparison to someone who simply isn't. (In spite of people getting ugly etc. over the years.)
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So, that's my rant. What are somethings you just cannot take seriously, and why?