The act of showing too much interest in another person making you appear desperate and less desirable to them. The term "Quick Sanding" is referring to if you were standing in quick-sand trying to get out- the harder you try the quicker you will sink.
Her: "I tried calling him, texting him, even went to dinner with his mom. Then I tried to add him on Facebook. I still haven't got any response. I know....I will try texting him again!"
Person listening to her: "You are Quick Sanding so bad right now- Please just stop!"
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?"