You can get arrested and convicted of attempt to commit most crimes. They don't have to be a "success" (completed) to qualify for punishment, although punishment for attempt is always less severe.
For instance, if I try to shoot another person and fail to hit the target completely, I can still be punished (attempted murder).
As for spraying someone with water, or throwing a tomato at someone, it is indeed a criminal offence ("legemskrænkelse" in Danish criminal law). Another matter is that such offenses are rarely reported and prosecuted, but they can.
If I was mistaken as to the grounds for your "Lulz" then my apologies