How do you know its a guy? What if its a girl that is talking about giving oral? Does that change things?
Also, I dont think (s)he is admitting to giving anyone oral. I think they're just making a joke, similar to the joke about actresses giving head to directors to get parts in movies. They're implying that if they had given head to the right person, they would've won the hand because they (person they blew) wouldve made it happen. So, they're implying that a) They gave the wrong person a Blackjack
or b) You gave the right person a Blackjack.
And knowing my homosexual-joking ways, I might say something like this as a joke.
"Whos **** do I have to suck to catch a 4 outer?" or something similar.