I think that if someone intentionally startles me, that can be an instant friendship breaker.  But at the same time, watching people getting startled is the only thing that makes me laugh
I would like to know more about this.
Simply put I just hate being startled. It's just really odd to me that I find it funny when I see other people getting startled.
It's okay for you to hate being startled, and you have a right to be upset when someone does that to you.  However, if you hate it so much, you shouldn't take pleasure in seeing the same thing happen to other people.  And if someone does startle you, they probably did it as a joke, since they also enjoy laughing at others, so you shouldn't break up a friendship over something that wasn't really done with malice.
You are talking about something that's not my intentions.
Your situation is definitely interesting. You should focus on how being startled isn't a good thing, and that may lead you to no longer finding pleasure in watching other people having to go through that.