The Sheldonian Orientation

[Kimk26]

I think, the first one that really impressed the socks off me was "The Loobenfeld Decay" (Season 1, Ep. 10), where Leonard lies to Penny to avoid having to hear her sing at a workshop stage production. Being that the lie involves Sheldon--and his conviction of it's implausibility--leads him to spend all of his energy on concocting an elaborate alternative in order to keep Penny off the scent. I think everyone did a great job in this episode. Most especially, Chuck Lorre, who wrote the story, and Bill Prady and Lee Arohnson, who wrote the teleplay. Every cast member had their place, and performed beautifully--including DJ Qualls, who played the dual role of Sheldon's drug-addicted 'cousin' Leo, but in reality, Toby Loobenfeld, a particle physics research lab assistant working with the guys at CalTech that Sheldon recruits for the 'role'. As Sheldon points out to Leonard, he's not only a physics major, but he minored in theater at MIT. To which Toby elaborates, "It's more of a double-major, actually..theater and physics. You can guess which one my bourgeoisie parents pushed me towards (as he rolls his eyes).

Yeah, I think it was this episode that sold me entirely on Sheldon. And yeah, the exchange between he and Toby, while arguing over what is 'Leo's' best character motivation in the deception, is what cemented it: 
Toby:     "Sheldon, how about this as my motivation? 'When I was fourteen-years-old, I was abused in the Philippines by a club-footed Navy chaplain'?"
Sheldon:  "No. We're going with 'middle-child, and a genetic predisposition to inadequate serotonin production.'"
Toby:     (Unconvinced) "Swell..how do I play' genetic predisposition'?" 
Sheldon:  (Sigh/roll of eyes) "Subtextually, of course."