My in-laws came to my parents house for Christmas dinner yesterday. You can see the pic of me in another thread I posted. My wife Karen was a bit concerned about what her parents would say. They'd seen me in a kilt before, but only once and it was casually. Her mom is a Russian immigrant and her dad came from Germany.

After they arrived Karen and her mom were standing off to one side while I was doing something. Karen says her mom whispered in her ear "my goodness, I didn't realize just how handsome he would look in a kilt".

Personally, I would have worn my kilt in your situation. It may have turned out the way my day did. And if she HAD laughed, oh well. Life goes on. I try not to let anyone dictate how I dress any more.