Kissing in school can get you in trouble with the authorities. This is because, you will have gone against the main purpose of been in that environment which is learning. Thus, for this you might be forced to undergo consequences like being expelled or heavy punishment.
Well, I'm not speaking from experience, but here absolutely nothing happens, except the teachers tell you to move to the wall instead of blocking the hallway. It all depends of the school and how heavily their rules are enforced.