What does shankapotomus mean?

Answer 1

A Shankapotomus is someone who loses a bet on a sporting event, but adamantly (and incorrectly) claims some technical rules violation by the winner and refuses to pay up.
In the famous E*TRADE baby commercial, Frank says, "But on the ninth hole, you moved your ball," thus implying that his loss was invalid. Since it is legal to take a relief from the cart path, Frank's objection is incorrect, so he lost. By refusing to acknowledge that he's wrong about the rule, Frank is a "shankapotomus."

The above definition has NOTHING to do with SHANKAPOTOMUS.
SHANKAPOTOMUS is actually a term used to insinuate that Frank hits a lot of SHANK shots, thus implying he's a HACKER. The SHANK is generally regarded as the most dreaded shot a golfer can hit. It is a shot where the hosel (heel) of the Golf club strikes the ball on the downswing, sending it sideways instead of propelling it forward toward its intended target. A lot of golfers don't even like to say the word SHANK.

Answer 2

Someone who "shanks", or mishits, a golf ball on a frequently.