Hitch is not a particularly good movie. There are a lot of problems with it, starting with no chemistry between the romantic couples and ending with a bunch of silly unfunny junk. But it does have one scene that is laugh out loud funny, and that is the Kevin James dance sequence. The reason the scene works so well is because James doesn't hold back. He fully immerses himself in the character and allows himself to be absolutely ridiculous. The look on his face as he performs the dance moves is priceless. It's a combination of fierce concentration and complete obliviousness, which is perfect for what he's doing. Will Smith doesn't do much in the scene, he takes the audience's point of view and stands around and mugs, but watching James let loose is just joyful. Because he's joyful, and you feel that, but he's also flailing around like an octopus on dry land.
This is what Hollywood routinely forgets. Funny comes from COMMITMENT. Commit to the idea, don't be smug or wink or any of that, just full on commit, and you can make it work. Don't? And you're going halfway.
Incidentally, this is why Stephen Carell is becoming a movie star. Because he commits to his characters, no matter how stupid or asinine, and he approaches the work with sincerity and focus. Comedy and drama are different in subject matter, but not technique. Winky smiley stuff is just surface funny. Deep funny comes from letting the audience laugh AT you, not with you.