How do you explain away stains on towels?

I laid out a towel on a folding table last night to have a place to set our hot dishes of food at the potluck. I wasn't eating anything as I am on a juice fast right now. Either way, the towel had a skid mark on it. I didn't see it before and I had just washed the towel. It was a white towel and the skid mark stood out. It definitely has to be my b/f because I always wash real good in that area, really lathering up and stuff to wash it out. Okay, to make a long story short, I said I dried off my car after I drove through a mud puddle. Either way, I don't think anyone believed me. I am going to be more careful in the future, but if it ever happends again, what can I say that will explain the mark? You have no idea how I felt when people saw that. I felt very humiliated.