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!"
Sandlin is an old Scottish word that is equivalent to modern day's use of Awesome.
To say someone or something is Sandlin, you are in fact calling them Awesome.
The term originated in the Sandlands of Scotland where the Sandlin clan was known as being the best of the best. The bravest warriors and the most beautiful clan's Men and Woman anywhere to be found!
You are so Sandlin, I wish I could be as Sandlin as you!