I picked up SIL this p.m. and the first thing she did after getting into the car was pull out a razor and start shaving her legs. I reacted, "Don't do that - it's dangerous! You can't do that in a moving car!" She replied "Oh yeah, I hate band-aids," and stopped.
I didn't bring any liquid in the car - I killed off my soda and dumped the bottle before I picked her up. The absence of drinks wasn't mentioned. When we got to the restaurant, I held on to my Diet Dr. Pepper for dear life, even taking it into the restroom with me, and drained it before we left.
She made a big deal about only having a box of Cheerios in her apartment and no money until Saturday, so I took her to Walmart. I spent $25 and she selected junk food and an $8 lipstick (she did ask if it was okay). However, as we passing the frozen food aisle I asked her if she needed anything to actually make a meal and she said she still had pot pies at home, but she didn't want to eat "just pot pies." I think after that, I'm going to limit myself to sympathetic noises when she complains about her lack of food.
When I got home, I told my DH about the dry-shaving attempt, and he said "You gotta be kidding. Who does that?" I said, "Your sister." He then muttered something about her being a weirdo and went about his business.