"Oh, hey guys, do you know I saw a guy with dementia?"
"Oh, hey guys, do you know I saw a guy with dementia?"
"Oh, hey, do you know I saw a guy with dementia?"
Listen up, buttercup. This "joke" is all about repetition, see? The joke teller repeats the same line over and over, just like someone with dementia might. It's kinda dark but also kinda dumb, just like you when you try to parallel park.