People who just keep yabbing despite you saying you need to go

It feels like any time I'm under some sort of time constraints or need to be somewhere by a specific time, if I'm in some sort of social setting it feels like there's always someone that won't let me go. The sort of person who will wait until you turn and start walking away to say "oh and...". Then proceed to do it two or three times until finally you have to almost aggressively tell them you have to go.

It may seem petty. But I feel I'm about to lose my shit at the next person who does this, no matter who they are or how long I've known them.