The Financial Permeability - S2-E14
Corrected entry: In 'Pilot' (season 1, episode 1), Leonard and Sheldon attempt to sell their sperm for money to install a T1 line in their apartment, and in 'The Dumpling Paradox' (season 1, episode 7), Sheldon says to Leonard "Frankly, if I could afford the rent, I would ask you to leave". Yet in this episode he says to Penny, "My expenses account for 46.9% of my after-tax income". The only way that his expenses could account for less than half his income just over a year after these lines can only really be explained away if the university gave him a pay rise of over 100%, which is incredibly unlikely for many reasons.
Correction: There are so many possible situations that could explain all of this. Regarding his payrise, You said "unlikely" but that does not mean impossible. That aside, Sheldon could have changed his spending/expense habits. Personally, I did when I got a payrise, regardless of how much it was. Also Sheldon has also proven to us that he is capable of making sarcastic comments now and then whether he is aware he is doing it or not.
XIII