Sheez! Don't beat yourself up! Taco Bell tacos only have 11 carbs each. I remember about 7 years ago when I first started low carbing, I would sneak off to Taco Bell and scarf a couple of tacos. It won't kill you, and sometimes it actually helps to shake up your metabolism. I know when I am in a plateau that I will cheat and eat a fresh peach, or maybe an ear of fresh corn. Somehow that seems to make me feel bad for cheating, but once I get back on track the next day, it seems to have once again caused my body to get back on track and start loosing again. I think the strangest thing is that when I cheat like this, the next am when I weigh myself, I either lost or stayed the same, then after stressing all that day, the next day I see the result of the cheating. Then the third day, I start to once again see significant results.
Good Luck, Remember, it is all about living and not always about loosing.