Wet Blanket

Someone who is pessimistic and lacks enthusiasm

Wet Blanket 意为悲观、缺乏热情的人

“James was not invited to go on the outing with the rest of the group because he's such a wet blanket. It's understandable that no one wants him around.” 

James没有接到邀请和大家一起外出，因为他是个让人扫兴的人。可以理解没人希望与他为伴。