'Pong' is the French interpretation of the 'bang' from a gun, therefore meaning explosive. 'Ass' is a commonly used word referring to being like one's posterior. So therefore, pong ass means:
Use 1) A person with explosive gas.
or
Use 2) A term for very good sex.
This can also simply be used as a random insult, as in example use 3.
Use 1) He is such a pong ass after eating fried food.
slip of the tongue perhaps,
Those idiots who drive around in a ridiculously raised pick up truck, making a top heavy vehicle even more top heavy and unstable
A:*gah*
B: "Whats the matter"
A: This dam prickup is blinding me.
B: Stupid thing's, as if there lights weren't blinding enough as it is.