My god, this. In ut99 we found, in the assault mazon fortress map, how attackers could shoot friends on top of the fortress roof from the starting point. It broke the map completely, but nobody cared. In fact, it was so cool, the defenders joined the attackers, landing on top of their own base.
There, changed it to the proper format.
I've seen plenty of glitches in LAN games with friends that were completely unfair, but never were a problem.