Am I being silly?

My bf came home from work and we got on Skype (we're long distance) and starts talking about how it's so funny that at work him and his friend had a "who's butt is better" competition. Basically they went around and asked everyone at work, including their manager, who's butt was better. I made a face like I clearly wasn't cool with it. I didn't say anything I just wasn't happy looking. Then I said I'm not trying to make a big deal here but I just don't like that. And he said you kinda are and I didn't respond so he just went to shower. Am I being silly to not like this?