A. Ask them to define the word "hoosier".
If you say that hoosier refers to someone from Indiana, you are from anywhere besides St. Louis.
If you say that the word hoosier means trashy or redneck, often associated with mullets, confederate flags, chewing tobacco, camo-wearing and a lack of teeth---you're from St. Louis.
It seems so mean when I try to explain it. People from St. Louis really don't hate Indiana, I swear. It's as if this slang has been around so long that people from St. Louis forget that it's also associated with an entire state.
I admit it, I use the word. Say it out loud. Hooooooooosier. It's fun to say. I just have to make sure that there is no one from Indiana around who would take it the wrong way.
Brittany looks totally hoose in this photo.
Besides that, I can't think of any other St. Louis specific slang. Some people do say "fardy" instead of forty, "yous" as a plural of you, and "warsh" instead of wash.
But I wouldn't recommend it---it sounds totally hoosier.