It's probably not healthy, but for whatever reason my proudest and most memorable moments tend to be derived from anger or revenge. I generally have a poor memory, but I always derive more joy from ruining somebody else's day than I do from quality playing on my part. If I'm greatly outmatched I'm more likely to truly enjoy the game when I can bring down somebody who is better than I am, even if I'm still losing overall.
In that vein, the proudest moment I can recall was in a team game of Sins of a Solar Empire. We were playing co-op and I happened to be in a bad spot - fairly close to an enemy, one that was aggressive and the 'strong opponent' against me. I got rolled, hard. I went down fighting but I was losing slowly, wasting all my resources on fleets that were just outmatched. I ended up creating a desperation fleet of a sort to pull back to an ally's turf, where I colonized a planet and everybody prepared for me to be basically worthless for the rest of the game, probably aiding in defense of the allies turf and that's about it because I didn't have many resources.
But my revenge gene kicked in - I was so damned angry that I just kept throwing myself at the dreaded archnemesis. Thing is, I play better angry. I had limited resources and knew it, but I was free of needing to worry about planets. Thus began the conquest via annoyance - outmatched in all regards, I was forced to do hit and run tactics with heavy emphasis on cap-ship special skills. Surprisingly quickly I discovered that I was actually winning battles, juggling multiple small hit-and-run fleets picking off any stragglers I could find and just generally messing with the mobility of the enemy and any new construction I came across.
Soon enough, I saw openings on a few planets and then everything just fell into place - I was so used to juggling the sheer volume of fleets that I managed to roll through the turf of my nemesis. There was much rejoicing when I recaptured my original homeworld, but unfortunately at that point I was in full bloodlust and didn't bother to consolidate my holdings. I kept my hit-and-run fleets in action, ignoring system losses, until I ultimately succeeded in wiping out my evil nemesis.
Once I did, I felt guilty that I'd left my allies hanging after they saved me...so I kept my hit-and-run groups going. I brought my harass and annoy party to the whole galaxy. Anybody who hit my allies found themselves beset by hardened, small groups of my ships. Out of sheer rage I basically broke the galaxy. It was glorious. I have no idea how I was actually managing that many fleets. I went from folding under assault from one enemy to fighting everybody else at once successfully. Now, granted, I did have help - the allies weren't doing nothing either and I would've been completely wiped out if not for them, but I went from almost dead to MVP in a remarkable way.
It's pretty deeply messed up that I rarely remember anything that doesn't make me angry, but...I sure did remember that one. Rage-fueled glory FTW.