The title refers to the expression "Double date" (or possibly "double take")
The title can also be a play on the words "double take," as in doing a double take when seeing something surprising, such as two Tates.
The one of two episodes with a rating of 9.2, the other one is Season 3 Oedipus Hex (1966), the highest rated episodes of the series.
In the opening sequence, Endora appears while Samantha is putting Darrin's name on a cake. As a result, Endora pronounces Darrin's name correctly for the second time this season. However, shortly afterwards she purposely bungles Darrin's name again: Darwin.