The marshalls said they smelled smoke and asked the man what he was doing in the bathroom. The Qatari said he was trying to light his shoes on fire.
No explosives have been found. The theory is the guy (between 25-35) was smoking a cigarette and was annoyed at being challenged.
My guess is he doesn't think his smart-aleck comment is too funny now. Likely he is the son of a powerful leader in Qatar, and he is going to be called home and have more than his diplomatic position removed. If he's lucky it will just be his money, power and pride. If they have had problems with him before, it might be his head.