Everyone has their weaknesses. For example, TheAbominatrix will start dry heaving if she sees you lick fabric. It's pretty fun.
So, basically, what are the things that are pretty much guaranteed to get the following reactions out of you?
Gag/Puke: Boogers not where they belong. If they're like in someone's nose then whatever, but like if a little kid has a green one stuck to their cheek I will die.
Cry: Like when there's an old couple and one of them dies. Ironically, if it's a young couple then it's quite likely I won't cry, but if they're old I totally will instantly.
Scream: Seeing a spider lowering itself in my peripheral vision. It always surprises me how I panic when this happens, 'cause rationally I like spiders. Last time this happened I shrieked and fled the room.