a popular german insult, "opfer" means victim. its just like you say looser, fag, retard, low life, freak...
if you insult someone with "opfer" you mean he's a victim and gets verbally "sacrificed" by you, which makes the others laugh at him.
how to pronounce: opfa (spell the "a" like ur from UK)
someone trips and falls to the ground.
you: opfer -.-