Evidently not a real sovereign state, however the word is a pun on the suffix "stan", which is common in Muslim areas. Sand nigger is a term used offensively against Arab and/or Muslim people. So it means generically an Arab and/or Muslim country.
"look, if Muslims and Arabs hate Western culture and still live here, shouldn't they go back to sandniggerstan?"
Bro 1: Bro! That chick was totally into you. She was hitting on you!
Bro 2: Nah man! She just wanted to allow me to let her use my scanner
Bro 1: What a scandigger!
A person who pads a handicap or acts as if he/she is at a lower skill level than he/she actually is so he/she can achieve better during competition that's handicapped or by skill level.
That sandbagger said his handicap was 20 strokes and he shot 10 over during the outing to win.