unperk

verb2

1. •
   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. — 1926
2. •
   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. — 2005