Corrected entry: For an obsessive genius Sheldon makes a stupid mistake when he blackmails Leonard into signing a new roommate agreement - any contract signed under duress is invalid. He gains nothing from Leonard signing the new agreement as no other action on his part is required. Effectively Sheldon has got his autograph. Big deal. Leonard is free to ignore the new agreement if he feels like it - and his lawyer was there to witness the fact that he was forced against his will to sign in the first place. This also begs the question of why Priya gets in such a panic about Sheldon blackmailing Leonard by threatening to reveal details of their relationship to her parents - why didn't she just advise Leonard to sign on the dotted line, explaining later that he signed an invalid contract? It would certainly have saved her a lot of grief.