Similar to LOL but i realised that when i am at my computer i generally don't "Laugh Out Loud". I kind of snort air out my nose and move my head back a little at the same time. Hence the term "Nose Snort Thing" or "NST".
When Someone Tells a joke that isnt that funny and you have to make some sort of a response so you dont hurt their feelings. Thats when you do the NST.