Probably quite a few of us here have fancied ourselves comedians at one time or another so I wonder if any others have awful stories from the stage.
I used to do a lot of theatre sports (would still like to actually) and of course you get things happening there like the awful time when during a scene (in a scored championship theatre sports contest game no less), my partner and I reached a natural lull in the conversation and both waited for the other person to say something. The silence just grew and grew and by the time we realised what had happened it was too late, the pause was already unaturally vast and awkward and we just panicked and froze and the silence went on for a thousand years. Eventually we both blurted out something lame and perfunctory and the scene, which been going well before, staggered to a laugh free conclusion. We lost the championship and that can't have helped.
In another game, we were told to work a soccer ball into our scene and, uncharacteristically, totally forgot and completed the scene without one mention of it. A judge said "Where was the soccer ball?" I marched out on stage and pointed at the empty floor and said "It's right there! Look! Do we have to spell out everything for you! Theatre sports is about your imagination!" and so on which got a big laugh but probably didn't win us points.
My worst experience though was during a round of World's Worst, a game where you individually step forward with a one liner example of the world's worst something. We were doing World's Worst Teacher and for the life of me I can't remember what my joke was, I must've blanked it out, but I remember what happened. I came up with the joke and said to myself "Gor blimey that's hilarious, what a cracker, this is going to knock them dead etc". So I stepped forward and delivered my joke and... crickets chirped. Nothing happened. Now what had happened is I'd simply died, happens to amateur comedians all the time, no biggy. That's not the problem. The problem is I was so over-confident about my material, I didn't realised I'd died. I thought they hadn't heard me. So after standing on stage to the sound of no laughs for a few seconds, I repeated the joke again in full, a bit louder. Again, no laughs. And then I did it in full a third time, louder still. I noticed people looking a bit concerned. It finally dawned on me that they had heard me just fine the first time and simply didn't think it was funny. I retreated back to the line-up and was a very quiet for a few decades afterwards. How humiliating.