Sarcastic

Being ‘smart’ in a way that some people would be say having a ‘smart mouth’
Saying something that you don’t mean or something that is the opposite of what you said that is sometimes stupid or dumb

Richard- is 14 years old
Debbie- is 30 years old

Debbie says, Richard did you take her clothes out of the bathroom
And Richard replies being a smart a**
Yea mom I took her clothes out of the bathroom, mhm sure did cause that makes sense.

Richard was being sarcastic because he was saying the opposite of what he did and being smart because his mom asked if he took a girls clothes out of the bathroom. Which makes no sense on why Richard would do that