Unfortunately, seems there are one or two obnoxious & arrogant tw.ts in the tower. While ago some prima donna cleared us (B747-4) for takeoff on 25L as a VERY heavy B747-4 started his rotate at the other end. I asked for a 1 minute delay, because, besides the obvious, it was a training flight (abinitio handling R/H), & was abruptly informed, that there was "NO SUCH THING" (his words, believe it or not), & that our in trail distance was sufficient. As we were light, elected to roll about 30 sec later anyway. Sent his supervisor an e-mail, with a detailed explanation about wing tip vortices, induced drag etc for his info. Nice reply received- from supervisor!!!!