What are good weapons for revenge?

ok well today me and my friends were walking home from school when this boy throws this mixture of chocolate sauce and maple syrup at us at us. it was disgusting and we have declared "war" with him and his friends. What are some things we can use (example- silly string, fly swatters, poop slingshots etc.) nothing that would like actually hurt them like baseball bats or anything... hahah. just things that would be perhaps painful.