A snooty "
liberal elite" type of person says this when he thinks something is "cool, hip, awesome or suave". Like when he cuts you off in his new BMW while you are driving in your old beat up Chevy. Biff would say to Chaz...."That was so money!"
When people say "That was so money", it makes the person
who said it look like a "phony" who's trying too hard to use modern,
new slang.