dead ass
To be completely and honestly serious.
A reply used by people who have been questioned on the truth of their comment.
To be truthful and not lie.
A truncation of the phrase “dead ass serious”.
Guy 1: Yo, swear I saw George (W.) Bush jump that fence for a corndog…
Guy 2: What? nah uh, you’re lying..
Guy 1: No, for real! I’m dead ass.