Worst PHP mistake for me was convincing the powers above me that PHP was better than Lotus Domino as a solution for what they wanted to do. They believed me, thanked me for my assessment, and quicker than you can say "for($i=0;$i<10;$i++)", they fired me (oops. Excuse me. "Laid me off"), and hired a young kid at half the salary.
I learned my lesson, though. "Always put your career before the greater good of the company."
Oh, and just to clarify... A "doh!" moment, to me, is something about which you can look back on later in life and laugh. Worst mistakes are not always "doh!" moments.
