Wiktionary
sore loser
n. (context informal English) One who complains or blames others for their loss.
Usage examples of "sore loser".
If I shout about the fact that they haven't answered the other two issues, I just look like a sore loser.
You get one free, on account of you're a sore loser but too old to learn any better now.
When Florida Secretary of State Katherine Harris was suddenly cast into the limelight because Al Gore was a sore loser, liberals promptly launched sadistic attacks on Harris’.