A boy who likes to tickle you could have a number of diverse intentions. Boys at different ages have different agendas. It could be that he simply likes you but doesn't know how to tell you. His tickling you could be his way of trying to get your attention. He probably just wants to say 'hey girl, look at me'. It's the equivalent of a little boy pulling a girl's pigtails on the play ground.
Sometimes the boy isn't interested in the girl at all, but loves the attention. In other cases, especially with younger, meaner boys, they tickle girls simply because they can. It's not the same as bossing over other people but it gives them a sense of control to see someone else helpless after all that tickling. If you are a boy, being tickled by another boy, then he probably wants to annoy you.
Sometimes the boy isn't interested in the girl at all, but loves the attention. In other cases, especially with younger, meaner boys, they tickle girls simply because they can. It's not the same as bossing over other people but it gives them a sense of control to see someone else helpless after all that tickling. If you are a boy, being tickled by another boy, then he probably wants to annoy you.