..and if you stick to it, you'll be golden:
Pick the kid you like the least and let him/her be the first to ride the tube.... start out slowly.. slowly speed up.. keep speeding up until you're redlining the boat.. Then cut the wheel as hard as you can, causing tube rider to cartwheel across the lake at about 60 mph.. Make sure all the other kids see it... My guess is that, if you do it right, nobody else will want to ride after that..
Friendship is like peeing your pants.. Everybody can see it, but only you can feel the warmth..