Supernatural is no stranger to meta humour, producing episodes all about Sam and Dean's lives being translated into schlocky pulp novels, but it was Season 6's The French Mistake which took this idea to the next level. Here the meta comedy didn't come under the guise of a wink and a nudge, as the in-show characters were transported to an alternate reality where their experiences are nothing more than a TV show.
Consequently, viewers were treated to scenes where you had Jensen Ackles playing Dean who was trying to act like Jensen Ackles playing Dean. It hurts to even type out the sheer layers to everything going on in some of these scenes.
The ep was a great send up to the fandom (with Misha Collins playing a version of himself who cared more about tweeting than acting being a particular highlight), while still being a solid monster-of-the-week case in its own right.
A premise like this could have gone so horribly wrong, but it's clear everyone involved was having the time of their lives, and consequently the audience did too.