I have a few:

-Glued on a portion of my wing and realized that it wasn't in the right spot. Put debonder on it and decided to help it along with a nice fresh exacto. Now I have a nice NIKE swoosh looking scar on the inside of my thumb. (had my wife hold the towel over my thumb above my head while I finished).

-Built my wing, made the hatches for the aileron servos, promptly realized that I had the wing upside down. Now I have top and bottom hatches.

-while applying the decals to my foamy, I meticulously applied the decals to the wing and made sure all the bubbles were out. Went to put it on the plane, now I can tell that I fly an EXTRA 300 from the ground (you got it, upside down wing again).

Seems I have a problem with wings.