I decided to just bump into Matt at the bus stop and continue bumping against him repeatedly until he yelled
Why would you harass Matt by bumping into him.
Matt's my best friend, but I love to mess with him because he is so sensitive.
It sounds like you want to hurt Matt. It is not okay to try and harm someone on purpose or to make them upset. You should talk about your feeling instead of playing full-body bumper cars with this guy.
Oh wow, you are a big softie. I love playing bumper cars without the cars!
Playing around and having fun are one thing, but hurting Matt by physically harassing him is harmful to him. Find some fun ways that you can both enjoy and spend time with each other that way instead.