Like I said in my earlier post, something like "troublemaker" or even really lean in and say "rabblerouser" or some goofy thing. Most seniors are NOT those things so the joke is clear. However, reality is that seniors are literally considered liabilities in many ways - insurance, etc. - because they are nearing the end of their lives so that takes away the humor (obviously my opinion since we are giving our opinions) when you use that word. Yes, I agree liability is a real thing, that's kind of my point in why my opinion is it's not very humorous.
Some people really enjoy hard deadpan humor or jokes where you have to decide whether they are joking or not. I prefer more obvious humor.