Dommy
Unremarkable User
I'm not sure if I'm interpreting these rules correctly but being friendly is only prohibited when it's done for an extended period of time and at that point, if it really begins to harm the match going on. The way I've seen it, simply high-fiving an enemy you come across or something like that, does not alone count as rule-breaking.
And what causes harm is likely to depend on what server you're playing on. I think actual friendlies should be completely prohibited from vanilla servers due to the overall nature of those servers, whereas there can be (and often is) a more tolerant attitude towards them in trade servers for example.
TL;DR ... Don't do it on those servers where the vast majority actually wants to play the game. Then it can cause harm.
And what causes harm is likely to depend on what server you're playing on. I think actual friendlies should be completely prohibited from vanilla servers due to the overall nature of those servers, whereas there can be (and often is) a more tolerant attitude towards them in trade servers for example.
TL;DR ... Don't do it on those servers where the vast majority actually wants to play the game. Then it can cause harm.