I bought 65 x 10y € swap contracts on the European ICE early mornings, must have been 2011/2012. Being tired and half-awke, I just saw the market was open and entered my order. What I didn't see was the bid/ask was 200 bps wide in pre-market. So I overpaid 100 bps on 65 contracts = down €65k. I remember talking a walk with the dog just to get some much-needed air in after that 
Luckily I was able to convince the broker to bust the trade an hour later. Whoever was on the other end was probably pissed.

Luckily I was able to convince the broker to bust the trade an hour later. Whoever was on the other end was probably pissed.