I'm going to be petty because I don't like this person.
Is that because you know the person very well?
Yes I know them really well.
It is rude to be petty about things that don't matter. People might avoid you if you act petty all the time.
I don't care. I'm thinking about just posting small little criticisms on their social media to mess with them.
Being petty with this person by making jabs at them on social media is not nice, and especially if this person is close to you. Put your serious nature above any pettiness you harbor.