@bigtiddyoneesan
Well, it's actually more like "be prepared beforehand for what's coming to you", though "for some reason" sounds cooler xD
I think they didn't specify it because they don't want to appear as bullies, I mean they have been acting as "friend"
@An0nim
Fair enough, I see what you were trying to do. I would suggest phrases like "You'd better prepare yourself" or "I think you should be prepared (for what comes next)," but nonetheless these are relatively trivial rephrases.