Never smoke inside a friends home. Walking down the street, the man walks on the outside of the sidewalk, preventing mud from being splashed on the lady. Never draw attention, be discreet in telling someone their zipper is down. Never use a mirror to check your teeth. Never apply lipstick or make-up at the table.
Guests can leave the reception after bridal couple cuts the cake.
Even then, make a discrete departure. No cell phones, pagers, beepers at the reception. Throw bird seed, blow bubbles. Must RSVP the wedding invitation. RSVP means respond if you please.