Easy one...
Playing right tape on the Angel field at the Toulouse World Cup last year, I go for a bunker, see a team mate go for the same one, turn back to the center, realise there is no real cover, turn back to the tape, trip over my feet that were still going left and slide out of the field on my face, losing my mask in the process.
Oh, how the crowd laughed. Still, we won and that's the important thing. I just felt like a t**t for losing my mask and sliding out in front of 500 people in Angel Heaven and the publicity tent.
I haven't done that again.
Wookie