To give someone the finger. To show someone your "Tall Can" is to stick your middle finger up at them, implying "Fuck Off"
Probably best known from Transplants - Tall Cans In The Air
"Duuuuuuuude, some guy just tried to rob Joey, he punched them in the face and gave em tall cans."
"Tall can" refers to a 16oz can of beer. Usually PBR (Pabst Blue Ribbon)
Has absolutely nothing to do with the middle finger.
I just had a six-pack of tall cans.