Walmart Trash
Similar to a Walmart rat. Someone who could be defined as Walmart trash spends their time in a Walmart and loiters around there. Another definition for Walmart trash is a Walmart customer who looks shady or is doing weird or stupid things.

So basically, it means a lesser human being that dwells in Walmart.
I was at Walmart the other day buying some snacks, but then some Walmart trash came up to me and questioned my snack choices.