'run like hell'. Basically, an faster way for a noob to cry to his noob-friends.
RLH can also stand for Real Life Hacks. This is used whenever someone does something incredible in REAL LIFE as in not on the computer.
Person one does a perfect back flip while avoiding getting hit by a rolling trashcan
Person two shouts: I CALL REAL LIFE HACKS!
(If it's on the internet and the video is not edited, person two may say "RLH" or "I call RLH".)