An acronym that stands for Rolling On The Floor Laughing My Fucking Ass Off.
It is meant to be used when the general, plebian ROFL/ROTFL, which is incorporated into the longer version, does not show enough snark, sarcasm, or general laughter over something that is genuinely funny. The method of use normally depends on the preceding sentence that this acronym is replying to. Tends to be used by folks who enjoy typing on cell phones and don't like poking all those keys to say what you mean. Can also be useful when used on Twitter, as it only uses 9 characters instead of 48 for the whole monty.
Iron Noder 2017