A Good Walk

Alright, listen up, you big ol' dumb-dumb! The speaker starts by saying 'this walk is really good,' like they're enjoying a nice stroll. But then, they have a sudden, terrible realization, and say 'Oh wait, you can't!' This means they are talking to someone who is disabled and physically unable to walk. The humor comes from the speaker's incredibly insensitive and awkward blunder. You, my friend, probably didn't even catch that the first time because your brain is smooth like a baby's bottom.