All the time.
A big example is when I talk to my crushes and then walk away thinking: "What the hell was I doing!?" Or when I fail a test.
Or today when I let the dripper in my chameleon's cage run too long and got water all over my desk, had to take the poor guy out of the cage, make him mad, clean the water, put him back and move his stuff around. :C I feel bad about it and I'm quite ashamed that I didn't realize how fast the water dripped out, lol.
Normally I get disappointed with myself after making a bad impression though.