unperk

Etymology

From un- + perk.

unperk means to make (someone) less lively or enthusiastic. Lexicurio rates it Rare gem — a strength score of 84 out of 100.

verb

To make (someone) less lively or enthusiastic.“I told him I was going into Stokenchurch in his Ford whether he drove me or not. He perked up a bit at that, but I pretty soon unperked him, and at last we got going on the road to Stokenchurch.”
To become less lively or enthusiastic.“[…] one single woman did perk up a bit, about there being a lot of single guys there, but then she unperked when she recalled that the cost of living is higher there.”