I'm sure I have plenty that I can't think of right now -- but the one that does come to mind happened in January.
My DH had found this pin he thought was really cool huge "15th Anniv" Coca cola pin at a flea market. We'd never seen it before (it was at least 3" square). We bought it and took it down to WDW in September. (I have since found out this pin is the centerpiece to the 15th WDW Anniv. framed Coke pin set -- someone must have broken theirs!). I liked it too, but thought it would be a great trader!
During one of the trading frenzies at Downtown Disney during our last holiday to WDW, a fellow wanted to trade me for it, and I ended up with a Donald Fastpass pin. I thought it was a cool trade because I had really wanted the Donald Fastpass. But after it was all over, I realized that my DH had REALLY liked that Coke pin and was someone disappointed that I had traded it for something less than a Jail Scene

.
Now, what you have to realize is that the pins are my craze, and my DH is EXTREMELY patient with me about all of this. He stands in lines for me, he carries my pinbooks around, he gets me sodas when I'm in the middle of a pin trading frenzy and don't want to leave, stands around Epcot with me for hours just watching in our 1 week vacation to Florida, and he even wears a lanyard. But when it comes to trading, it just isn't his bag (but did I mention how patient he is???

)
He never SAID not to trade the pin, and he NEVER said he was disappointed I'd traded it, but I could just tell by looking at him. I felt so stupid that I wasn't picking up the signals -- the one pin he really liked and I swapped it out.
I wouldn't have traded it if I had to do it all over again.
Who's next?
Jan