Doing a Cullum

To claim you wish to do something, then proceeding to get distracted for upwards of fifteen minutes before remembering the original task at hand.

Cullum: Hey do you want to play a game in a minute?

You: Yeah sure
*Cullum doesn't come back to his computer for half an hour*
Cullum: Sorry for the wait I went to the shop.

Cullum: Want to play a game after I've finished my work? ETA is 10 minutes.
You: Okay sure
Cullum: Be right back I'm gonna get a coffee before we start
*Cullum has actually gone to the pub after disappearing for 20 minutes*
You: Looks like he's Doing a Cullum