I'm so sorry that your stuff wasn't treated properly. I would not let them borrow them again and be up front about why. If they take offense, just ask them to respect your opinions, that's all.
Personally, I trash my bags, I have 2 LV's and some others and they get everything on them. Last Saturday night, my I spilled a margarita on my Damier Hampstead (I did clean it right away though), but I have a soy sauce spill on the inside and some nail polish on the handle.
I figure it's ok if I trash my own stuff, but no one should disrepect someone else's property that way.