Ignore it and shrug it off the first time, but if she starts doing, um, other things then you should probably tell the principal.
i would like to point you to several news stories this year
The question is why
Doing this could cost the teacher their professional and personal lives. It is not at all right to do this for playful reasons.
its illegal to kiss a teacher unless your over 18.....just saying.......you shuould kiss a teacher because then you might get him/her in trouble