I'm going to get petty revenge
Why do you want to get petty revenge?
My friend dissed my new clothes style.
It sounds like your feelings got hurt when they dissed your clothes. It might sound like a good idea to get revenge, but maybe you can talk to them and work it out.
Nah, I'm going to get my revenge, time to annoy and harass him.
It's wrong to harass him because you are feeling spiteful. He may not even realize that you were offended by his words. Talking it out would be more productive.