Yeah Nux is having fun all right. He’s waiting for Slit to become tired, for his arms to become loose and wobbly and absolutely useless. It’ll take a while, but as soon as Slit collapses Nux will have his pants off and fuck him into the ground while he’s too spent to push back. Slit knows this, and he relishes in pushing his body into doing more reps than it should be capable of, because 1; Nux goes at him rougher and harder the longer he has to wait, and 2; he really really likes the feeling of not being able to get up when he’s being pinned down (but only when it’s Nux who does the pinning, and he’s never ever going to admit that to anyone.)