I think this is a good point. Would it be offensive to sing "Does your girlfriend know you're here?". No. So why is it offensive? Surely if there is pure equality and no prejudice singing "does your boyfriend know you're here?" should be just as banal. There's an argument that claiming it is homophobic just perpetuates the marginalization of gay people. Surely whether they have boyfriends or not is irrelevant? Also worth pointing out that what people will do/say in a large group can be very different to what each individual would say.
Pretty sure it's offensive because it gives the idea that they think there's something funny and mock-able about being gay.
It's not an argument but a thought. I worded the initial question poorly by making a comparison when it's a separate question on its own. I do wonder whether it would help if heterosexuals who are called gay or the other variety of names try not to react in a negative manner and brush off low level "Banter" with a whatever.
I think the stigma associated with homosexuality is a symptom of society's inability to deal with sex openly, its not only homosexuality its all sex. The vast majority of offensive comments are or were sexual taboos. There is perhaps more fear of homsexuality but society as a whole does not trust its sexuality and so there is conflict within most people about sex and that conflict spills out into our daily lives in the form of sexism, homophobia or whatever else.