What excuse can I make for my rhinoplasty?

I've heard someone say "I wanted to change my nose so I had it fixed." Her tone was dismissive and she just moved on to other topics. It worked very well. Fixing a deviated septum doesn't change the exterior of your nose, so if you wanted to go that route you could say "I had a deviated septum so while they were fixing that I asked them to fix the outside as well". Remember that even if people treat you cruelly, you're going to be moving away in a few years and soon almost nobody will know.