well this is a hard topic. because there is nothing you can do to make it hot. but the only thing I can think of is if they get caught on his foot or something don't laugh and make it awkward. but be aggressive like you want them off now! guys don't really care they just want to feel as if you want it so if its a show or you really do always act like all you want is him.
Start kissing him from his neck all the way down to where the zipper starts...then use your teeth to slowly pull down the zipper but look at him in his eyes with a seductress stare to show him that you want him...then just pull his pants down slowly with your hands