How about this then;
09R for departure, a BA 767 crossing a the far end. A 777 has been given a line up and wait, and is just crossing the Cat I bar. I turn around to co-ordinate with ground, and then look at my strips to check on slots, SIDs etc, to decide on my order. I look up to see the 777 on the roll passing 40-50 kts. Quickly check the BA 767 has vacated, which he has. I go in to clear the 777 for take off, and just as he is rotating he replies: "Roger, we are rolling".
Doh! <img src="eek.gif" border="0">
Gonzo.