Mr. Monk Goes to Mexico - S2-E2
Trivia: According to co-producer Tom Scharpling, the Mexican homicide cops are purposely written as parodies of Stottlemeyer and Disher, right down to their attitudes, their ranks, their suits, and Captain Alameda's mustache. Even the bumbling lieutenant's name is a little joke on Disher. Plato means "dish" in Spanish.
Answer: Notice also that in the opening credits scene when he is touching parking meters her also wipes his hand on his clothes each time he does it.