Sour loser 

Sour loser means when someone is angry about losing and doesn't take it well, taken from the phrase sour grape and is pretty similar to sore loser

You're just being a sour loser because you lot to a 4 year old

Sour loser by Crazy blue 0104 September 2, 2019

sour loser 

The origin of the word "sore loser". This much makes more sense than using the phrase with a "sore" in it. Sour comes from the phrase, "Sour grape". A big misconception of that figure of speech.
To whine or sour grape

Derick is such a sour loser, that he slams the plates in the gym, because his team lost the finals.

sour loser by Craig Thomson October 2, 2013