Chatty people who don't pick up on the increasing facial, body language and verbal cues that I'm not in a chatty mood.
"Blah, blah, blah....etc"
Avoiding eye contact "Yup"
"Blah, blah, blah....etc"
Noncommittaly "Uh-huh" eyes still fixated on whatever I'm focussed on such as the paper, the monitor...etc.
"Blah, blah, blah....etc"
"Uhm....oh, look at that time" said awkwardly looking at my watch in feigned surprise, "I have to get going", as I prepare to leave the room on some imaginary task
"Oh, OK....see you later...and bye the way.....Blah, blah, blah....etc"
....As I realize I am actually going to have to cut this person off and say "I have to go now!"