Firstly, imagine the squeaking. Now keep that level of squeakage in mind while surveying the below. It can only add to the comedy factor. As for what exactly Zac is doing thrusting his leather clad nethers into Ellen's personal space; he's a) promoting Dirty Grandpa (much like Aubrey Plaza discussing Robert De Niro's shy nipples over yonder) and b) trying desperately to make everyone forget about that Gawd awful MLK quip. 

While Zac is more than happy to lap dance, it seems the twerking is a step too far for him, as he cradles his head in his hands. Suck it up, fellah, you've got a film to promote - DANCE MONKEY, DANCE etc.