bully

I have a male fancy guppy named "Zippy" in a tank with 2 mollies and 3 platys (he had a guppy friend once upon a time). He is ALWAYS chasing the platys (all male) around the tank, especially "Argo" who is twice his size, and nipping at his size. Is this normal fish antics or is my guppy a bully?

I've had these two fish for about two months now. and just recently saw the dalmation molly nipping at the balloon molly (which has since been in the corner of our 10gal tank). AND the balloon molly has lost color on the top. is it stressed out? i don't know their gender but i think she's a...