A foreigner who has incomprehensibly heavy accents.
This term originates from this particular group of foreigners' speech pattern. As they request favors from you, they often complete the request in a polite way of saying "Thanks" multiple times. However due to the inability to annunciate the /θ/ th sound in "thanks", they end up saying "sanks sanks sanks sanks sanks", similar to the sound of a tank firing its machine gun.
B : "Sure"
A : "Sanks sanks sanks sanks sanks!", and walks off
C : "What did sanks tank ask you to do for him?"
B : "I have no idea, I can't understand a word he said"