Wiktionary
pick on
vb. (context idiomatic English) To bully, harass or make fun of a victim; to bother or harass.
Usage examples of "pick on".
Here am I, serving Clayton's cigarets - I don't know why I pick on you, Clay.
Don't go out on the street like a sheeting fool and pick on a street-sleeper in filthy clothes.
Fantasizing about impalement, flaying, and disembowlment while he sat in a hovel with nothing to pick on but flies.
If you're going to try to get away with something, why don't you pick on some greenhorns?
Sometimes a bully tried to pick on me, but the moment I started to fight I showed him a lesson.