This can be done just by people watching.
But if it happens to be a slow day here are a few suggestions that will spice up your visit.
1) While walking around the store, sing in your loudest voice possible "I smell sex and candy".
2) When someone asks if you need help, begin to cry and ask, "Why won't you people just leave me alone?"
3) While handling guns in the hunting department, suddenly ask the clerk if he knows where the anti-depressants are.
4) Hide in the clothing racks and when people browse through, say things like "pick me!! pick me!!" and scare them into believing that the clothes are talking to them. (This is an oldie but goodie).
5) Take up an entire aisle in Toys by setting up a full scale battlefield with G.I. Joes vs. the X-Men.
6) Get boxes of condoms and randomly put them in people's carts when they don't realize it.
7) Go into the dressing room and yell real loud "Hey, we're out of toilet paper in here!"
Thank you, Walmart. For your well stocked shelves, low prices, greeters who smell like my grandpa and the ability to keep me constantly amused over the years.
You complete me.