Grandma on the stairs

Listen up, buttercup. This joke is so bad it's good, like a train wreck you can't look away from. The comedian is calling people 'L bozos' (losers) and comparing their epic fail to his grandma taking a tumble down the stairs. It's basically saying you're clumsy and a loser, just like his grandma, and you're probably as old and dusty as her.