it gives plus 10 ap and -2 damage threshold

how much is -2 damage threshold and how much of a difference would it make?

also for four eyes do helmets that have holes like the cover art one do those count as glasses?

Probably not much of a difference. I'm actually going to pick Built to Destroy and Kamikaze as my two traits.

I would only take it if you're going to be using VATS constantly so the damage reduction keeps you from dying. -2 Damage Threshold means whatever armor you wear will allow 2 more points of damage to your HP. The best armor in the game prevents damage up to 28 points. With Kamikaze it will be 26 points, meaning it's 14% less effective.

7% less effective. 26 is 92.8% of 28.