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"

There are always alternatives.
                -- Spock, "The Galileo Seven", stardate 2822.3

Yow!  We're going to a new disco!

If the colleges were better, if they really had it, you would need to
get the police at the gates to keep order in the inrushing multitude.
See in college how we thwart the natural love of learning by leaving
the natural method of teaching what each wishes to learn, and insisting
that you shall learn what you have no taste or capacity for.  The
college, which should be a place of delightful labor, is made odious
and unhealthy, and the young men are tempted to frivolous amusements to
rally their jaded spirits.  I would have the studies elective.
Scholarship is to be created not by compulsion, but by awakening a pure
interest in knowledge.  The wise instructor accomplishes this by
opening to his pupils precisely the attractions the study has for
himself.  The marking is a system for schools, not for the college; for
boys, not for men; and it is an ungracious work to put on a professor.
                -- Ralph Waldo Emerson