I can nominate myself for rushing into the water last time at Wraysbury without checking my kit.
Then imagine my surprise when I shutdown my right post and breathed the reg down. Now, alternate into gob...b0ll0x where on earth is my alternate?

I was Mr Smooth&Calm and just reached back and turned my air back on, but too late, I never got away with it because everyone but me knew what was about to happen 'cos they could see I'd screwed up!
(Thanks Garf & PeeBee for sorting me)