I like the expression "It's like shooting fish in a barrel." Example: If someone says to me, "I like collecting the bottletops of different beers I've had," I reply, "It's like shooting fish in a barrel." And then the other guy will go, "Oh, you think it's an easy thing to do?" And I say, "No, I think it is a very strange hobby that's probably not too fulfilling or enjoyable." I think I use the expression improperly.