Disco mud
The thick black, mud-like substance found late in the evening in most bars and discos that is the result of mixing cigarette ash, sweat, spilled drinks and various other dubious substances together and mixing it well with the feet of drunk students. Is one of the few substances known to man that can never be removed from clothing.
I got disco mud all over my jeans last night. Now I have to throw them out, otherwise people will know I was on my knees in the toilets.