.this is caused by his penis pushing air into the vagina during intercourse. .it is quite normal, even if a little embarrassing for some women. .my boyfriend laughs it off every time

Yep! Good old vagina farts. Also known as queefing (kweefing, who knows?), this is pretty darn common and... well, the only real thing ya can do is just laugh it off. It's how a woman's body is built; air gets up there and it has to come back out some time.