I love this, because I've witnessed at least half of these first-hand.
"Someone buying beer and diapers." I actually accompanied someone at Wal-Mart while they purchased alcohol...and diapers. Never viewed it as comedic, but it's pretty funny now.
"Obese person using a scooter." These are my favorite. But in my town, they're not just at Wal-Mart. They ride dirty all around the streets of town...right to the traffic stop. Much like a 21st century Frosty the snowman.