I'm pretty sure this word refers to ice cream. Either that or the actual meaning is so sus that I can't describe it in full detail.
Person 1: Oh man, I can't wait to try out this fellatio!
Person 2: AYO!
Person 1: What's wrong with me trying out ice cream?
Person 2: You'll know when you're older.
Similar to the term used for a TV that is "cable-ready" or "HD- ready", "fellatio ready" is a term used to describe a girl who is so hot, she's ready to be orally sexed at any given moment.
STEVE: Hey Carl, did you see that hot waitress at Sonic last night?