Hux, with his conservative Imperial upbringing, perceives Kylo as the peak of sexual deviance; the perfect example of that disgusting (fascinating) “New Republic Sexual Decadence” he was warned (fantasied) about. The Republic tempter come to lure and defile Good Citizens. Kylo, knowing himself to be moderately kinky at most, finds this hilarious and runs with it. After all Hux gets this riled up over a little spanking and some after-blowjob cum-stained kissing, just imagine the possibilities.