Derp Gun - A gun that causes a lot of damage with one shot, usually having a very long reload time and low penetration. Usually associated with short, High-caliber guns that load HE. Artillery guns are not considered derps (e.g. the 'derp gun' on the USSR tank KV-2).
The joy of the derp gun, is like the joy of s*x, but with explosions.
by Slagger42 May 16, 2014