Is having one friend be a T and the other innocent wait till everyone is dead then killing themselves against the rules. Be aware they do not kill eachother at all.
If you communicate to one another one of you is a T and the other is innocent through means of communication that is NOT in game chat, then it is against the rules and is considered ghosting. BAM
Ok i will explain it spesifically just to make sure 2 people (names will be mentioned in a report if against rules) talking to eachother in pub chat about whos left, 1 is a t the other innocent. They won't kill eachother nomatter what. As soon as the innocent is told hes the last one he suicides. Is that against rule?
A traitor and an innocent purposefully not killing eachother is considered metagaming and is against the rules. See here: http://www.seriousgmod.com/threads/a-guide-to-sgm-extended-rules.12605/#post-109983