Why did dally harass cherry and Marcia

Dally bothered the girls because he liked them..... and also because he knew they were involved with the Socs. He wasn't the kind of guy who ignored pretty girls..... neither was he always nice to them. Dally is the epitome of the "bad boy".

Dally sees it as an opportunity to make trouble. Also, because of the ongoing fued between the greasers and the Socs he wants to harrass them.