No, you aren't being oversensitive. He's being inappropriate.
While it's nice that he considers you a skilled fellatrix, for him to discuss it in public is, as you said, juvenile and degrading. For him to continue to do so even after you've objected is completely selfish and disrespectful.
What you two do in the bedroom is no one's business but your own. It's called intimacy for a reason: those are the intensely personal, private experiences shared between two people that make their relationship unique and special to them. Those are the moments that belong to them and no one else. I'm not just talking about sex here, either, but anything private that bonds a couple together, like her insecurity about growing up poor or the time he cried like a baby when his dog died. To make that kind of private information public belittles its importance and shows disrespect for your partner and your relationship.
You realize he's not really bragging on you, right? He's bragging on himself. He's saying to his friends, "Gentlemen, I am the proud recipient of high-quality oral sex on a regular basis. Aren't you? No? Well that is a shame." Your boyfriend is, as the saying goes, rubbing their noses in it. It's nothing more than schoolyard one-upmanship, and at the expense of your dignity. If his true goal was to compliment you, he would stop mentioning your sexual skills in public once he knew you felt degraded rather than complimented.
I wonder how he would like it if, in front of him, you told your friends something like, "The boy sure knows how to eat an ass, let me tell ya!" or "I keep telling him it's okay that his penis is small because it gets REALLY hard"? Something tells me he wouldn't like it much. Also, does he not realize what his friends immediately visualize when he talks about your blow jobs? That's right -- you giving them one. Is that what he wants? I doubt it.
If he wants to compliment you on your oral skills, fine -- he can do it in private. If he wants to compliment you to his friends, he can brag on your intelligence or character or how you are a wicked striker on the soccer field, not your tits or your ass or how well you blow him. Otherwise, tell him to get used to saying to his friends, "She used to give me great blow jobs," because there won't be any more of them.
Cary... you're on the $$ on this one...
JDV, I may have a new crush!
Ugh. How creepy that he even did this in the first place, and for him to continue with it after you told him how you feel about it is completely out of line. Cary's answer is right on target. This is a matter of respect and trust. Your boyfriend has no respect for you and can't be trusted to keep private things private. This sort of bragging would make anyone feel violated and used, and rightly so.
Yes, he IS out of line. However, one thing you could do to get him to STFU is to offer your excellent talent to his friends. Just agree with him next time he brings it up, and tell whoever he's talking to that you'll be glad to show them.
On the other hand, you could just dump him. If he doesn't care about your feelings any more than that, he doesn't deserve you!
He probably doesn't think it is as big of a deal as it really is. He is a guy and probably has no idea how his comments make you feel. That said, he is very immature for making comments like this in public and with you present. This is the type of guy who needs to be validated through his friends. He was probably not taught how to respect women when he was growing up.
Do yourself a favor and dump this guy.... there are plenty of respectable fish in the sea.
She told him exactly how his comments make her feel. It doesn't get any clearer than that.
...fellatrix.
goddamn that is good.