Combination of the word double and the phrase
lol, referring to something too amusing for the mere
lol and thus calling for the more powerful "doublol". Used most commonly shortly after someone has already replied to a previous statement with the less powerful
lol.
Brant: So, I saw Alyssa and
Josh earlier, I guess they're dating...
Matt: LOL
Brant: And somebody told me they were even engaged too...
Matt: DOUBLOL!!111!1