After Clark comes back, he's either not at full strength or they discover something like Black Kryptonite. Either way Clark gets drunk for the first time, maybe on some of the expensive stuff Bruce can afford. He ends up being the most charming and cute drunk ever. Bruce is highly amused, until Clark comes onto him and starts telling him what he wants Bruce to do to him, like whispering the raunchiest things in Bruce's ear.

It's through sheer will that Bruce resists, but he's there to take care of Clark when he experiences his first hang over, and then they talk feelings.