OK, locked and loaded - Time for a quick rant!!!
The only real Cruiser I would consider a girl's bike is a Virago, but only because they're made for small riders.
Don't make the mistake a lot of people do by thinking that Cruisers are for short people. They may be lower to the ground, but the distance from seat to the controls is what matters most.
The 650 does very nicely for anyone, regardless of gender. I ride one and so does my Mrs. She is 5' 4" and can comfortably reach the controls, but anything bigger would need altering.
TBH, unless this boy of yours is riding a 2300cc Rocket III, he too is on a girl's bike and I can bring a good hundred female riders to the argument who would kick his arse on whichever bikes they ride. The new Honda Fireblade is a tiny bike (far too small for me) so it must also be a girl's bike, despite it's insane speed, right?
I know it's only in jest, but if anyone dares criticise your choice of ride, they can fuck right off. If he has a problem with what you ride, then he can pay out for whatever he thinks is a more suitable bike for you....
Of course, being a woman, he will 'decide' that the most suitable bike is the one you wanted in the first place, right?