Last night I was snuggled up in my comfy chair, my feet on the ottoman, sipping a nice if pedestrian white wine, and reading about the geometry of vectors in the plane. When the concept of the polar form of a vector came up I got slowed down a bit (and I was going pretty slowly as it was). I read, and re-read, and stared (as if I were bringing the words into focus rather than the concepts), and I came to the horrifying realization that I remember absolutely no trigonometry to speak of. I may be breaking the law of cosines at this very moment and I wouldn't even know it.
Fortunately this doesn't seem to matter much for my purposes (which, in general terms, is to understand what people are trying to do when they use matrix operations -- or, at a miminum, to pick up on the terminology in a more than perfunctory sense). But there was a moment when I thought I'd have to pay my high-school-senior mathwhiz friend Gretchen to tutor me. That would be a tad humliating for me, although I'm sure it would please Gretchen no end (as it would give her ample opportunity to roll her eyes at the general thickheadedness of the adult population).
[Update: Hey, no fair! Somebody's already taken eigenvalue as a username.]