When you get the gun in the first Portal...
"...do not touch the operational end of the device. Do not look directly into the operational end of the device. Do not submerge the device in liquid, even partially. Most importantly, under no circumstances, should you..FEUHWSIHEWL."
I know that the Portal team probably didn't have this idea when that line was written, but I like to think that GLaDOS was going to say something like, "Most importantly, under no circumstances, should you aim the operational end of the device in the direction of the moon."
Just a thought. ;)