Sheldon hires some guy to pose as his cousin, Leo, to pretend to need an intervention for Sheldon to avoid going to see Penny in Rent.
Sheldon has one of his co-workers post as his non-existent cousin, Leo, in order to get out of seeing Penny in Rent.
Leonard attempts to talk his way out of going to see Penny in Rent after hearing her sing off key.

The Big Bang Theory Season 1 Episode 10 Quotes

Sheldon [knocking on Penny's door]: Penny, Penny, Penny...
[Penny opens the door]
Sheldon: Good morning.
Penny: Do you have any idea what time it is?
Sheldon: Of course I do, my watch is linked to the atomic clock in Boulder, Colorado. It's accurate to one-tenth of a second, but as I'm saying this it occurs to me once again your question may have been rhetorical

Sheldon: I'm uncomfortable having been included in your lie to Penny.
Leonard: What was I supposed to say?
Sheldon: You could have told her the truth.
Leonard: That would have hurt her feelings.
Sheldon: Is that a relevant factor?
Leonard: Yes.
Sheldon: Then I suppose you could have agreed to go.
Leonard: And what would I have said afterwards?
Sheldon: I would suggest something to the effect of, 'singing is neither an appropriate vocation nor avocation for you, and if you disagree I'd recommend you have a CAT scan to look for a tumor pressing on the cognitive processing centers of your brain