A little off topic.

I'm teeny. I have dietary restrictions and trouble gaining weight. It's not exactly fun.

I've found, usually at work, and usually older ladies, love to comment on it. But without much context, so I'm not sure how to respond.
I ask them how many in their party - "YOU ARE SO SKINNY!" Okay... is that a compliment? Just an observation? Do I say thank you?
I had one lady actually grab my arm as I walked by the other day, "You are just so thin, you're making me think fat!" Okay, should I apologize?

I know they don't mean to be offensive, but good golly, would I love to give a smart comment.

I worked an extra couple days in a row this week and I am truly beat. I am going to relax SO HARD the next two days. And eat tons of junk food :)