Carlton Banks can be a guy who is completely oblivious to all signals, innuendos, and other hints from girls. Like if his girlfriend called him at 2 am to come over for a "cup of coffee" he'd be like, "Sorry, I don't drink coffee this early, but I could come over around nine and play Scrabble with you if you want, and then maybe we could cuddle."
A Carlton Banks can also be a guy who seems to make up a bunch of stupid excuses to not have sex with his girlfriend. Like, "I feel like it will mess things up," or, "I'd rather just cuddle." While cuddling is nice, SO IS SEX!
Basically a Carlton Banks is that "sweet but stupid" boyfriend who you often suspect might be very very gay.
Carlton Banks: "Yeah I am pretty tired. I think I'm gunna go home."
Girlfriend: "No one is gunna be home until way later tomorrow, do you wanna just crash here?"
Carlton Banks: "No thanks. I like waking up alone in my own bed."
Girlfriend: "Oh ok... wait what?"