> if somebody gives you a gift you knew was coming and pretend you're baffled by its appearance

I never know what to do when somebody goes through a lot of trouble to surprise me, but I figure it out anyway. Usually I play along and act surprised because it makes the other person feel good.

Imagine your girlfriend was planning a surprise birthday present for six months and somehow the secret leaked. You saw an open tab, or one of your common friends spilled the beans, or whatever. Are you going to ruin her excitement about surprising you just because "feigning surprise is bad"?