Snipping out large chunks of unrelated material isn't really a troll trademark, but doing a little "creative snipping" or "quote forging" is, such as something like this:

You're stupid

> You're stupid
Yeah, because you're such a genius, doofus. Duh!

>> You're stupid
> Yeah
Glad you agree!

I.e. snipping to change the meaning of the posters post.