[Big Red Badger]

Now I need to know What Episode of
Star Trek that clip is from!!!

[Steely Tom]

I suspect it’s from a “blooper reel.”

[mairdie]

I think it’s from Turnabout Intruder, the last episode in the last, third, season. A crazy female wants Kirk’s job and decides the way to do it is change bodies with Kirk, so Shatner plays a man/woman trying to mimic Kirk’s mannerisms, but who is still uncontrolled crazy, and the guest plays a woman/man with Kirk’s instinctive mannerisms. It gets sorted out by Spock mindmelding the woman and recognizing his captain.

[Telepathic Intruder]

I’m pretty sure that’s the episode with Lord Garth, where he changes into Kirk’s form but realizes he can’t fool the Enterprise crew into beaming him up. “Whom Gods Destroy”, episode #69. You can’t watch them for free on the internet anymore, though.