ungentlemanly weapon
(n.) any weapon that is designed to cause damage to anyone, regardless of whether they are general public or paid military. This includes all chemical and biological weapons, nuclear, and any other WMD. The weapons not included in this are those such as firearms, stabbing and blunt objects, hand grenades, fists and canons.
World War I was considered to be a gentleman's war until the German army tried out it's chemical weapons once stalemate had been reached.
ungentlemanly weapon
n. Slang for the male genitalia
Yesterday, on my date with Joey, he showed me his ungentlemantly weapon