This is one of the reasons we sold our last house. Our neighbor insisted he bring his motorcycle into the house (living room) and then clean and start it. (we lived in a townhouse) We complained to everyone we could think of to do something legally about it (this was not the only idiotic thing he would do but that would be hijacking the thread). Point being there are idiots like this out there. I did love the karma part though thank you for the laugh.
Yeah, this one is an urban myth, has been running around for years. Still good for a laugh, but not true.
If the guy were sitting on the toilet, with his pants down, and tossed the cigarette in, it would probably "whoof" and burn his butt, but that's it. It actually takes a LOT of gas (in a gaseous state) to actually explode, rather than just puff up a lot of flames, and a rag in the toilet, partially submerged, would not allow accumulation of that much gas.
Even if it did explode, his pants would not be blown away, they'd have been protected by the front of the toilet bowl, even if it did shatter and blow outward.
If it did explode, it would not have blown him out the bathroom door, it would have blown him upward - explosions happen in the direction of least resistance, in this instance, straight up.
The reason urban myths catch on, is because they have something in it that makes you WANT to believe it is true - your feelings about dumb guys, your feelings about big business, your feelings about crime, etc. They put a hook in there that makes you want to believe it enough to not examine it too closely and see the illogical parts.
A little logic applied will often prove what is a myth, and what is not - just like the dumb one about the cockroaches at Taco Bell - so completely stupid that anyone who actually THOUGHT about it would know it was not true.
Oh, and my kids often accuse me of being no fun, because I cannot restrain myself from pointing out that they really didn't use white flour for everyday bread during Laura Ingall's time (Little House on the Prairie TV series), that married women were NOT allowed to teach school in the 1800s, that IV therapy would NEVER be used in the old west (the "Love" series), and other inconsistencies in movies, books, etc.
Sometimes an analytical mind is NOT a blessing - spoils our enjoyment of things we could otherwise be innocently entertained by.
But then again, it sure helps when explaining political lies...