I have many moments where later I think, "Der! That was stupid." But, they are usually only a couple hours delay between the incident and the realization. This example brought to you by the letter "x" took a good 8 years.
I'm not going to announce my email address, but it is through xmission.com. Haven't heard of that? I'm sure you haven't, it's been my parent's isp for the last decade and I have kept it after moving out because, well because I'm lazy. So, here's my "Der" moment:
Realizing, for the first time, when giving my email address of dancer...@xmission.com to a cute clerk at a store that it kind of seems like a stripper email.... Oops.