"Buckwheat" is the wild haired character who played in "our gang" a 1930-1940 tv show.
"Beaver" is a slang word for a woman's vagina.
When the two are combined you can automatically get the mental image of a crazy haired vaginal area.
Wow trim that automatically comes to mind.
Billy: Did you go downtown last night?
Jim: Yah, but not worth braggin' man that shit was a buckwheat beaver, bro!
Billy: Are you serious?
Jim: Yeah, I'm still pullin pube's out of my teeth!