1) Pick any integer. Your partner picks an integer without knowing yours. The first person to think of a number says "clomp". They are locked in. The other person can say their number any time after "clomp". Honor system. No cheating.
2) If your number is less then your opponent, but not one less, then add your number to your score.
3) If your number is one more than your opponent, then add your number and your opponents number together and add it to your score.
4) Otherwise no score.
5) First to 21 or more wins.
+I may have stolen this from Martin Gardner, I honestly don't remember if I came up with it or I read it. My brother came up with the name "clomp".