With the pool one, I find it funnier to not introduce the challenge and to do it twice. Be like, "Watch, this." Knock it over. Then say, "And to prove it's not luck," knock it over again. "See great right?" They will be unimpressed and not sure what exactly what you even accomplished. You explain that both times you knocked it over. They will still be unimpressed. Tell them its harder than it looks and bet that they can't do it. You could even make it a 2/3 to win scenario have them fail on the first, win on the second, and lose on the third.
