Are you talking to me?
I hate it when I go up to someone I know and start talking to them only to realize that they are on a freakin' Bluetooth call. DRIVES. ME. INSANE.
I'm talking and wondering why they keep saying "Yeah. I know" at random moments in the middle of my sentence. Then once I realize it and say, "Oh, excuse me." they don't interrupt the phone call to acknowledge me or say hello.