I'm usually that asshole who buys a bunch of ice cream, puddings, sugary cereal, and a fucking salad.
One time I had a huge cheat night planned, bought a bunch of cookies, ice cream, cereal, chocolate bars, and one banana. I was checking out at the grocery store and the cashier was like "...and ONE banana?" I was like "gotta keep it healthy!"
I used to notice what others ate/bought but I don't anymore. I just can't be bothered to care, unless the person buying is morbidly obese, then I wonder. For example, we have a lady at work who's huge 250lbs minimum and about 5'3". Every lunch she eats a small salad with some chicken and an apple. That's it. So I always wonder what the fuck she eats when she gets home to maintain her physique.