Can I tell my cousin that his girlfriend is crazy?
How is that girlfriend crazy?
I don't want to put it very simply but I heard she was cheating on him and she's hot.
I'm sorry, but just hearing rumors is not enough to call someone out. You need to respect her and your cousin's relationship or you might ruin it with your baseless lies.
I'm not going to call someone out, I'm just going to say she's crazy.
You don't know that she is crazy, and you're hearing rumors that you have no evidence of. Your cousin will be very angry with you if these rumors turn out to be untrue, do you want that?