Let me start.
When I was 17 I played in a London Schools' bridge tournament. The general standard was, ahem, well I can't lie, it really wasn't that good. On the final board, you pick up
LHO opens 2C and partner passes. RHO thinks for a few seconds, his eyes flitting between his cards and his bidding box. And then, without warning, he tilts his bidding box over and *plop* all 35 bidding box cards thud on to the table. He had bid 7NT.
After checking that we were all using the same pack, I doubled very quickly and led the club ace (Yes, I was paranoid about them having 13 top tricks!). Dummy meekly tabled
The plump young man's face was a mixture of shame and horror as he said
"Sorry partner, I thought we were playing Weak Twos".
To compound the misery declarer had a singleton club and after 5 minutes, intermittently painful and embarassing, punctuated with laughter, we chalked up 1700.