Get to the point, James...we know John likes to read everything on the Internet and we already know he is a little light in the loafers.
Anyway, John stumbled across some information that sheds a little light on why they call Daniel a neck slappa. Apparently, the gay gang has some f'ed up type of initiation involving what would amount to a sexual assault and neck slapping is slang for what would be the equivalent of the jumping in portion of the initiation.
I'm looking now to see if Gangland has an episode about these guys yet, but this explains quite a few things.
And hopefully if you've read this far you know this is completely made up (except I'm sure John probably was reading up on the cosmetic products). I honestly have no clue why Daniel is the neck slappa, but I hope you enjoyed my rendition of how it might have happened. Happy April Fools' Day!