Here's my worst moutain snafu:
One day I wanted to climb Pagoda Mtn. in RMNP. I arrived at the Glacier Gorge TH very early, where I met a couple of guys getting ready to climb Chiefs Head, and was at Black Lake before sunrise. I got into the upper basin below the West Face of Longs to find that I couldn't make out any of the peaks - they were all shrouded in clouds down to 12,000'. The clouds looked non-threatning (stratus, not cumulus), so I continued. I looked for the gully between Longs and Pagoda, and headed up. The talus was very loose and the climbing much more difficult and less pleasant than I had expectd from Roach's description in his RMNP guide. About half way up, the two guys I'd seen at the TH caught up to me and informed me I wan't where I thought I was - instead I was in the Pagoda-Chiefs Head gully. So I climbed Chiefs Head and headed down with the other guys toward the Stone Man Pass route. I descended to the lake, and then saw the sun break through the clouds to the north. That is, what I had been thinkging was the north. That was alarming. Turns out I hadn't gone over Stone Man Pass, but had descended to Lake Powell in the North Inlet drainage rather than Frozen Lake where I though I was.
It was a long way back up over the pass, down to Black Lake, and out to the TH. After that I decided to invest in a compass and consult the map more diligently.
I still haven't climbed Pagoda.