I'm going to make petty comments about my best friend and her boyfriend
Why do you want to be petty towards your friends?
I'm petty by nature and I like to reinforce the fact that my friends are assholes
If this is how you feel about these people, then it sounds like they aren't really your friends. If you can't keep these comments to yourself, maybe you should stop hanging around with these people.
It's just petty things, nobody will notice.
Unfortunately, your friends and their boyfriends will notice these repeated comments that you make. They could resent you for it, so if you still want to be their friends, you should stop being so petty.