Some of the answers I'm proud of:

• https://stackoverflow.com/questions/4550937/how-to-force-update-when-doing-git-pull/14359894#14359894
• https://stackoverflow.com/questions/1083955/how-to-get-difference-between-two-dates-in-year-month-week-day/17537472#17537472
• https://math.stackexchange.com/questions/1091908/how-to-stop-forgetting-proofs-for-a-first-course-in-real-analysis/1092902#1092902
• https://math.stackexchange.com/questions/617625/on-familiarity-or-how-to-avoid-going-down-the-math-rabbit-hole/619259#619259
• https://academia.stackexchange.com/questions/7602/what-should-raise-red-flags-to-detect-fabricated-data/7609#7609
• https://tex.stackexchange.com/questions/109969/how-to-practice-latex/110002#110002

And an answer which I'm not particularly proud of, but which quite a few people seem to like:

• https://stackoverflow.com/questions/18955384/how-to-convert-keyvaluepair-to-dictionary-as-todictionary-is-not-available-in-c/18955562#18955562