Was I really being stupid?

So I have always told my boyfriend he was sexy on a regular basis and had written “my God, you are so damn sexy” on his bathroom mirror where he writes motivational quotes and whatnot.
This morning, he was telling his friend who had told him he had lost some muscle how he’d miss his chest and how he hadn’t worked out much, so I said “I still think you are extremely sexy”. Then he goes “no offense, Babe, but I don’t care what you think. It’s more about what I think, isn’t it?” so I said, “fiiiiine!” (neither of us had a(n) serious/angry tone in our voice) and went to the bathroom and erased what I had written (again, I was not acting mad/sad/offended, but was smiling and being playful).
Then, he goes “Stop being a butt hurt. That was really stupid. You will soon make me really mad if you don’t stop being a butt hurt.” so I said “Hey you said you didn’t care about what I think! smile But he kept calling me stupid, and told his friend who was in the bedroom with us what I just did.
His friend goes “yea, that’s really stupid.”
and he goes “It’s almost flight-worth stupid”
I didn’t say anything but in my head, I was like, “Are you serious?!?! You guys are almost attacking me. Why is he (my boyfriend) doing this?!”

So guys, what do you think? From a guy’s point of view, was I really the one being stupid? I really don’t understand…