There is little doubt that the 'str8 dude' is on a power trip. There are loads of guys out there who get a huge ego boost by discovering that you want something and that they may be in a position to deny you that... It really does not have to be sex at all.
I am all for trying and NOT giving up easily. But there is a limit to how far anyone should really go. Feeding his ego does no one any good. Even the guy who seems to be enjoying denying it, is actually getting a totally wrong message, too.
More likely than not, his next victim will simply shrug with his shoulders and move on to the next perfectly willing guy who'll be more than happy to trade off a solitary jerk for a good, hot mouth...
KD