Spoilsport (noun)

1. A person who ruins the fun or enjoyment of others, often by being excessively critical or by not participating in a group activity.
2. A person who is excessively critical and tends to spoil the fun and enjoyment of others.

Origin:

The word "spoilsport" is a combination of the words "spoil" and "sport", it refers to a person who ruins the fun or enjoyment of others, often by being excessively critical or by not participating in a group activity.

Examples:

1. He was always a spoilsport, always finding something to complain about.
2. She was such a spoilsport, she never wanted to join in on the fun.
3. He ruined the game for everyone by being a spoilsport.
4. The spoilsport is the one person that no one wants to invite to their party.
5. The spoilsport's attitude was a real mood-killer.