Be more polite.
Over the last 10 years, Sheldon learned the hard way that being polite is vital to any friendship. (Most recently, the "hard way" happened when Leonard rubbed his naughty bits on Sheldon's apartment flag.)
But take it from a mysterious drifter named Theodore (and played by Christopher Lloyd)—treating others the way you want to be treated is preferable to grinding their gears out of spite. There's a reason they call it the Golden Rule!