The anti-lol is used as a means of expressing the lack of humour in a situation. It is best used at times when someone tries to make a joke on an IM and fails miserabley either becuase : 1) They are morons 2) They just arent funny
The anti-lol is believed to orignated around 200BC in in a small greek province and is a direct descendant of the word LOL
Here is an example of when an anti-lol should not be used:
Dude 1 : Heres a really funny Joke... How many babies does it take to paint a barn?......
Dude 2 : Dunno
Dude 1 : Depends on how hard you throw them
Dude 2 : HAHA That is quite funny. This situation in no way requires me to use an anti-lol