PORTER: Drink, sir, is a great provoker of three things.
MACDUFF: What three things does drink especially provoke?
PORTER: Marry, sir, nose-painting, sleep and urine. Lechery, sir, it provokes, and unprovokes: it provokes the desire, but it takes away the performance: therefore, much drink may be said to be an equivocator with lechery: it makes him, and it mars him; it sets him on, and it takes him off; it persuades him, and disheartens him; makes him stand to, and not stand to; in conclusion, equivocates him in a sleep, and, giving him the lie, leaves him.
– William Shakespeare
Macbeth, Act 2, Scene 3. The Porter tells a dirty joke about drinking and sexual performance to Macduff, who is not very amused. The Porter is gate-keeper to Macbeth’s castle. He provides important comic relief in a play that is filled with tragedy and violence.