WASHINGTON - It is the charity stunt that has got everyone from billionaires to pop stars and even former US presidents drenched by buckets of freezing water. But don’t expect American diplomats to get involved in the fast-growing Ice Bucket Challenge - in support of Lou Gehrig’s disease research - any time soon. The State Department has issued an internal telegram forbidding US ambassadors and other high-profile foreign service officers from participating in the forfeit, in which people either pledge $100 to ALS research or record themselves getting soaked by frigid water, then post it online and challenge others to do the same.