"How many hors d'oeuvres you are allowed to take off a tray being
carried by a waiter at a nice party?"

Two, but there are ways around it, depending on the style of the hors
d'oeuvre.  If they're those little pastry things where you can't tell
what's inside, you take one, bite off about two-thirds of it, then
say:  "This is cheese!  I hate cheese!"  Then you put the rest of it
back on the tray and bite another one and go, "Darn it!  Another
cheese!" and so on.
		-- Dave Barry, "The Stuff of Etiquette"