Optimist primus

Someone who is delusionally optimistic about a clearly bad impending situation.

Maddie: Do you think Chester the bunny will make it?
Joe: Ab-so-fucking-lutely. I only nicked him with the weedwacker/bunnynicker.
Maddie: But he hasn't breathed in more than a week.

Lisa: Joe, I think you're Optimist primus.