I've let a friend who weighs in at about 285 ride my Tiger. He doesn't look out of place and though he's a Harley guy, he said it was the most comfortable bike he'd ever ridden (of course, he'd ridden nothing but Harleys).
Seriously, ride what you like. I rode with 2 brothers who were about 5'9" and 320 lbs. One rode a CBR 600RR and the other rode an Interceptor. Sure from behind they looked like they were wearing mechanical thongs, but they had fun.
Don't worry about it.
