The theory that the phrase "lol?" can be used in response to any typed phrase on the internet, no matter what it is. This is mainly because you cannot express emphasis on the internet.
It is the ultimate end to the "o rly?" chain of words. It can be used in any position of the "o rly?" chain, but is most often used after "no wai!".
Some have theorized that "lmao?" can possibly be used in this situation, but its been agreed that "rofl?" is not possible to use in any situation. In rare cases people use "lqtm?" but that is used mostly by fags, but also by Dimitri Martin.
This is the easiest way to piss someone off on the internet: Just reply "lol?" to whatever they say