ZD: “Giggling and Laughing can be done deliberately. People can do silly things. And there is definitely more room to say that laughing in public is more untznit than ankle boots”
In that case, the same rule would apply. It certainly seems likely that deliberately laughing in front of your principal after she specifically made a rule against it could possibly constitute “zilzul morim”. I would think that a girl who did that should have it in mind when she says “al cheit…b’zilzul horim u’morim”.
Interesting maaseh that is connected to this topic:
When R’ Shniur Kotler zatzal came to the US, one of the first things he did was to find his former Melamed and to ask mechila for the fact that when he was five years old he misbehaved and taunted his Melamed by saying “my Totty is a bigger Talmid Chacham than you are.”
Of course the melamed had not been particularly offended by being told that R’ Aharon Kotler was a bigger Talmid Chacham than he was, but apparently, R’ Shneur felt it necessary to apologize. (heard from the Melamed’s daughter).