This is very common amongst bunnies and in 90% of cases it means they want you to squirt pee back on them. Occasionally however, often during their hormonal period (about 8-12 weeks of age), urinating on their carers means they would like to partake in sexual activity. I know that my sound strange but just like humans approaching puberty, rabbits get sudden sexual urges. These can be sustained by entering your pinky finger only, into the rabbits anus for a period of about 2 minutes.

There! Now your rabbit should stop peeing on you!