Sex you don't want anybody to know about. It has to be kept on the DL because of any number of reasons: you're embarrassed (coyote ugly), you don't want your boss to know, you're a cheating bastard and you don't want to get caught, etc.
"Yo, Smiles, did you hear that Mr. Ed and Toto are having secret sex?"
"No way Ldog, that isn't happening!"
"Oh, don't worry, it is. Apparently, Mr. Ed is afraid his boss will find out. As if Quatals would give a shit!"
A written request to have sex. Exactly like a booty call, but via email instead of the phone. We all know that sometimes you can't call (if your boss is near by, etc), so you issue a booty email instead.
1) Booty Email time: 4:30pm. Meet me in the janitor’s closet at 5:05pm.
2) Booty Email time: 2pm. I want to come over to your place at 10pm tonight to get laid, will you be home?