The act of getting it on with a girl/guy from a country other than your own. The qualification is that he/she has to be born in the country you want to lay a claim to, and ethnic heritage from there is a plus.
Made popular by Roosh V, traveling author extraordinaire.
"I just got my Chinese flag."
"But dude, Li Lu grew up in Cupertino."
"Doesn't matter, she was born in Guangzhou."
Text sent at 3:56AM: "Chilean flag"
Text received at 3:57AM: "Congrats fuckface, i hate you"