Squarehead is a late 19th century ethnic slur directed at German and Scandinavian immigrants. The phrase is meant quite literally as a disparaging reference to the cranial features, though often just used as a generic ethnic slur against those groups.

Basically the stereotypical shape of a Northern European's head was thought to be square- so it was (and is) an insult to call someone with that ethnic makeup squarehead.
Kid: "Mommy, did you see how weird that Norwegian's head looked?"

Mother: "Yes dear, the fucking Squareheads do have unusually shaped skulls. The Swedish have even more box-like heads... don't even get me started on the Danes or Germans..."
by LickMySwedishMeatBalls April 24, 2010
1. In the 'olden days,' some Scandinavians were condidered -- by some Americans of the time -- as beleiving what was told them, being rather naive in worldly matters and being somewhat easily conned and deceived -- and consequently, were occasionally referred to as 'squareheads.'

2. A late 19th century ethnic slur directed at German and Scandinavian immigrants to North America.
Used a coupla times in that great 1980 film. "The Long Riders" by Randy Quaid's character, Clell Miller, "damn squareheads," when referring to Minnesotans.
by RC135M October 24, 2010
A derogatory nickname for Germans during World War I, when Germany was our enemy. They supposedly had large, square-shaped heads. See kraut.
It's not nice to call Germans squareheads.
by bstokes June 13, 2006
Most Germanic types: another synonym for Kraut; Another Hated nationality.
by J.M. Reiter June 21, 2003
A type of person without a sense of humor and unable to enjoy a sense of humor.
"What's the difference between a wife and a girlfriend? 45 pounds!"
"You're fuckin stupid man."
"Yeah well you're a fuckin' squarehead."
by Dave January 17, 2004
a boy who likes melody and is a gameaddict
Chris is such a lame squarehead.
by law345 March 19, 2009
a person who is extremely cheap. Often of Germanic or Eastern European descent. Behaviours often include pack-rat stockpiling of useless items, refusal to throw things out, and salvaging things from the garbage.
My mom is such a squarehead. She won't let me throw anything out.
by BSKM February 17, 2009