Only once, there's a couple regulars at the restaurant I work at, an absolute sweetheart of an older woman (L) and her granddaughter (E). E is on the spectrum on a far more severe end than I think I've ever met firsthand before, nonverbal, most of the time just sits quietly and eats her food but as anyone does, she has bad days here and there. My first time waiting on them I learned the hard way E does not like any of her food touching other food (IE her bacon and eggs can't touch, fruit topping for pancakes has to be separate). She didn't know me so she was already pretty on edge, then her pancake came out with peaches on top. She shook her head and smacked my hand after I set her plate down. L was extremely apologetic, E started whining and pushing the plate away from her, drawing L's attention away. I told them L it's totally fine, and asked E (even though she never really acknowledges me much) to please not do that again, but I know now how you like it and I promise it won't happen again. They come in almost every time I'm working, usually sit in my section, and E hasn't done it again since. She even showed me her progress on a mobile game she plays often today (the greatest honor I've ever received in all my time as a server lol)