Star Trek TNG S2E20 The Emissary
A really enjoyable, solid episode, exploring the Klingon psyche somewhat through the rather fine device of a half-Klingon, half-human woman who gets to describe how it feels to Troi, to act as foil and lover to Worf, and generally make jokes about it.
Very well-written, hanging off a slender premise that allows it to run at the subject without much diversion, and thankfully no silly subplots to detract.
Another very fine episode from the rollercoaster that is season 2.