Most of the time Bruce's mouth is the only part of his face that Clark gets to see. Over time, he develops a bit of an oral fixation. Bruce's smiles, smirks, Bruce drinking, Bruce with a tool between his teeth while he fixes the Batmobile, blood on Bruce's lips, Bruce licking his lips ...

Maybe five times Clark got distracted by Bruce's mouth? Or just one time, I don't mind either way. :D