Cover-Up
Man, this trick has saved me so many times.
Man, this trick has saved me so many times.
Black Hat and Danish are trying to clean up the mess that some bloody murder most likely performed by them has left. This story may thus be a continuation of 515: No One Must Know.
Another guy, Cueball, is on his way home and is about to arrive just when they are finishing the clean up. But then Black Hat realizes that the ceiling has also been stained (by the violent murder...) And now they do not have time to fix it.
But Black Hat knows how to deal with the situation, and when Cueball comes home, he says: "Did you know 'gullible' is written on your ceiling?"
Gullible means easily deceived or naive; an old and simple prank is to make an unlikely claim related to the word "gullible". For example, you might claim that the word "gullible" isn't in the dictionary, or that someone wrote the word "gullible" in the sky. The notion that you're deceiving the other person is embedded in the claim, so if they believe you (even for long enough to check), they're labelling themselves as gullible.
Here, Black Hat uses the existence of such pranks to his advantage. When he makes the claim, Cueball immediately catches the joke, and deliberately avoids looking at the ceiling, to prove that he wasn't fooled. Of course, preventing him from looking at the ceiling was the entire point.
The title text is hinting that Black Hat has had to cover up killing people several times as this trick has saved him many times. Of course there could also be other things than blood that he had to hide (the money he just stole, drugs, etc.)