If I'm overwhelmed by it I'll naturally start tuning them out and start thinking other things. When they poke me and say "do you know what I mean?" I usually say "I'm sorry what did you say?". They get visibly frustrated and have to repeat themselves. I actually try to listen, but when they continue droning on, my attention wanes. When they poke me again because they see my focus has drifted, I'll ask them to repeat it again. When they get fed up and say "but you're not even listening to me", I respond with "you're talking a lot but you're not really saying anything". Sometimes they acknowledge this, sometimes they get upset. Hey i tried being polite.

Btw sometimes I'm the one talking too much but I look for visual clues and stop talking if they don't seem interested.