Buy an AR with the brass deflector built in. I have shot tons of stuff and I'm left handed.
The only problems, Sling points on an MP-5 and quite a bit of the German equipment are all right handed only. Most tactical/side sling stocks are for righties. Clearing a jam on an MP-5 is a bitch for lefties.
Some pistols, namely Sig products hard hard to use controls for lefties.
Benelli shotguns have reversable safeties, warn you right handed friends, when they grip your lefty gun they can accidentally move the safety without noticing.
Shooting some subguns, especially open bolt guns can result in a face full of burnt powder and splatter, wear your shooting glasses.
I try and shoot mostly right-handed stuff except bolt rifles. It helps to be used to the controls.
I do want a Randall "Port-sider", it was a reversed 1911 pistol from the 70's that never really took off. I think it would be fun to loan it to folks without saying anything and let them figure out the problems.