To have fun, frolic and romp about in a slightly mischievous way.

When your so pissed off from losing multiple amount of games that you play worse and worse till your so pissed you begin leaning over your keyboard screaming over every little mistake you make and complaining about gaming imbalances

(Common in Starcraft II)

When someone does a harmless prank.

When you don't have anything particular in mind, but are looking for an entertaining adventure.

To be silly and playful.

To be in an unsober state of mind, and walk aimlessly looking to interact with any and every person in sight. To lose track of the friends you were originally with and find new ones.

To do a Larking is to wander around aimlessly in your workplace, chatting to anyone who will listen to you in order to avoid your duties in your workplace as much as possible.