苛める(いじめる) Bully someone, verbally or physically.   $$$
ちゃかす To take something that someone just said in earnest, and turn it into a joking matter.
ふざける Joke around with, usu. In a friendly way
やかす(ひやかす) Tease, usually about “Oooh, Sammy’s got a giiiirlfriend!” “No I don’t!!” “yes you dooo!”
からかう Mess with someone’s head.
がらせ(いやがらせ) Harass in a stalker manner.