"Poodle shooter" is a derogatory term for the M-16 and M-4 family of rifles with which the U.S. military is armed. This stems from the fact that the M16, M16A1, M16A2, M16A3 and M16A4 (the "M-4") fire the 5.56mm cartridge, a cartridge that many soldiers and Marines think is underpowered for combat operations. Prior to the Vietnam War, the Army and Marines were armed with he M-14 rifle, which fires a much more powerful cartridge, the 7.62mm NATO round. During the Iraq War and the war in Afghanistan, the M-16 and M-4 proved to be inadequate to the task of longer-range combat engagements and the M-14 rifle was brought out of mothballs and issued to some units.
"Man, this M-4 sucks. Did you see that? I hit that hajii at least three times and he just kept running!"
"I know. The M16 is such a damned poodle shooter. It would be embarrassing except our lives depend on these shitty rifles."