A person who has a very large penis.
When a group of friends go down to the swimming hole, the bankwalker is a person with a large penis who, after getting naked does not get in the water but prefers to "walk the bank" to show off his stuff
Look at that bankwalker over there, he's such a tool
but damn, he's hung.
Typically a southern (US) term. When in high school, and a group of male and female friends decide to go skinny dipping at the lake, invariably the most endowed male member of the group will walk up and down the bank, whilst his donkey schlong sways to and fro, searching for the optimal spot to enter the water, thereby flaunting his manhood to both male and female members of the group.
At the lake on Saturday night, Sally cheerleader fell in love when she saw Tim, the football team’s quarter back and bank walker, swinging his man meat while looking for a place to dive in.