Get rekt Grunkle

As a lesbian in can say that this is 100% true and I regret having to sacrifice my cousin too the gays

An old man suddenly realizes that his life as a heterosexual male was a complete and utter lie. His time traveling granddaughter has shown him the way. He begs for a chance to start over. She grants him that chance...and fades out of existence.

What episode was this? I've seen them all but don't remember that

take back the rainbow