I think the main problem with some of the more ardent roleplayers is that they tend to take themselves way too seriously. If they could losen up a bit and try to apply some humour to the absurd situations that sometimes occur in a Mud, they would do not only their co-players but themselves as well a big favour.
If a Mud contains combat code that allows you to score exp. points from killing mobs, obviously some players are going to kill those mobs. If you cannot handle that without sneering at the players that do, you should find a mud where all actions, including combat, are emoted.
A fact is that quite a few Muds that announce themselves as RP mandatory still have a strong element of hack'n'slash, and this sometimes can lead to funny situations. The example below is from Threshold.
(Disclaimer: This is not meant as any flame over Threshold, which I actually think is a pretty good game, in spite of my frequent clashes with Aristotle on these boards. It could have happened in any Mud of a similar type. Anyhow, here goes
One of the Newbie areas in Threshold is a small farm with some chicken and cows and other animals, that you obviously are supposed to kill. I was in a room with a cow. I was not 'interacting' with it (not even in any indecent way), just studying it, contemplating whether or not it would be safe to kill.
Now in Threshold you don't see the name of other players until you have introduced yourself to them (a somewhat lengthy procedure, but very IC). So in from the left comes a player, who on my screen looked something like 'a brown-eyed Dwarf' since we hadn't been introduced. Next this Dwarf opens his mouth and says:
'Fair maiden, would you mind if I kill your cow?'
Sure - it was bad roleplay. But after all, the Mud WAS RP enforced, and he obviously didn't want to take any chances, in case some nitpicky imm was lurking in the background.
And it gave me one of my best laughs on line that week.