1. A humble, yet funloving individual whom of which rides skateboards in empty swimming pools and surfs waves in any/all oceans throughout the world.
2. A person that is secure enough of their self to openly make fun of their self, character, etc.
3. (adj.) A common word used to describe a typical surfer or someone that surfs.
"Look at that guy over there laughing his arse off... he's just sumdumsurfer."
A very hairy man who rides skateboards and surfboards, enjoys barley pops, the color orange, and likes using the word "feckless". Can be seen in his natural environment of the ocean or skatepark sporting his man-sweater.
Dude, Sumdumsurfer is da mang!