I'll stick with comedies, because top 5 of all movies is just brutal. Hell, many movies or actors can make their own top 10. So yeah, 5 random, awesome scenes.
The Jerk, "He hates these cans!"
Animal House, cafeteria scene.
Something About Mary, franks and beans.
Breakfast Club, Bender under the table.
Princess Bride, battle of wits.