This Bottom Man definitely knows how to give his Top Man (the guy who's fucking him) so immediate and erotic feedback on how well he's being served. To begin with, they're both keeping eye contact which is always a plus when you're making love (or lust).
His facial expression, in addition to the eye-to-eye contact, is showing his Top Man exactly how good it feels to have his massive erection probing deep inside his ass. That and he's giving him the added pleasure of feeling his arm muscles flex with each generous stroke of his cock entering his ass!
He's also giving him a full view of his hairy armpits. Most men, myself included, enjoy watching another man flex his armpits and show-off the manly hair that grows inside. His Top Man obviously is liking this because now he begins to feel his chest and play with his nipples!
This is working for the benefit of them both as they're now about to nutt (cum, ejaculate) into paradise! Dayum, dudes!
Take care and stay proud and bare!
ReNude Pride
