Yet if the boyfriend silently suffered all of you would say to tell her. Grow up people he didn't do anything wrong. No one is 'grateful' for bad sex. He said it creeps him out, and asked her to stop. He gets a vote on how he wants sex too.
This is tough, namely because I had one solitary experience during which the woman screamed like a literal banshee and freaked me the fuck out because 1) I thought I was hurting her and 2) other people can hear that shit and may think I'm raping the chick.
My best advice would be to talk to him about it. If he has unreasonable expectations, then ... well, you know what to do.