Gene has been pushed up against a wall before, his wrists restrained, and used as something to be dominated and have power asserted over. He's been thrown down on a bed and pinned and violated while he screamed. He'd had his head held down and been forced to swallow; and all of these more times than he's cared to count.

But he has never been kissed before.

He could push Tony away, but he doesn't. While he has the ability to kick Tony's ass six ways from Sunday, he knows in his bones that's more trouble than it's worth. He knows what he needs to do.

So he goes completely passive. He doesn't fight, but he doesn't return the kiss, either. (Partially because he doesn't know what to do there.) He's been in this position enough times to know that it's easier if he just goes along with it.