In context|slang|lang=en terms the difference between fat and shank
is that
fat is (slang) an erection while
shank is (slang) to remove another's pants, especially in jest; to depants.
As nouns the difference between fat and shank
is that
fat is (obsolete) a large tub or vessel for water, wine, or other liquids; a cistern or
fat can be (uncountable) a specialized animal tissue with a high oil content, used for long-term storage of energy while
shank is the lower part of the leg; shin.
As adjectives the difference between fat and shank
is that
fat is carrying a larger than normal amount of fat on one's body while
shank is (slang) bad.
As verbs the difference between fat and shank
is that
fat is (archaic) to make fat; to fatten while
shank is (archaic|ulster) to travel on foot.