OP I am going to buck the trend and say YANBU.
Fuck that for a joke, bride's big day allows her to act like uptight bitch.
When I got married I remember my main concern was that everyone was enjoying themselves. I would have been more concerned by silence than a jovial back slapper talking a bit loudly.
Imo a good wedding is one where there is plenty of good food and alcohol and the guests make an effort to talk to people they don't know and to be in a convivial party mood.
So to my mind, your DH was fulfilling his part of the deal in making the attempt to talk to people he didn't know and was probably a little more loud than he is normally as freely flowing alcohol can have that effect on one, also when we are trying hard to be our most sociable selves.
Most weddings I have been to, and indeed my own, include musical performances where the guests continue to chat whilst listening. I mean it's a wedding, not a concert hall performance. So to not be immediately aware that you were meant to be silent is not that strange imo.
If the bride wanted the guests particular attention at the point of her cousin's performance she should have had the MC announce it with the instruction for shush!
But to single your DH out with the demand to be quiet was very rude imo.
And although I probably would have acquiesced and wouldn't have stormed out it would make me view the bride differently and not in a positive way!
Couldn't she have had quietly drawn DH to one side or tapped him on the shoulder and had a quiet word in his ear asking him to be silent and listen please? Or better still, asked one of her bridesmaids or whoever to do it?
Anyway I agree with you OP ignore all the other uptight bitches on here 