As a mod, in such situations, I tend to use whatever I consider necessary and sufficient to encourage better behaviour in this respect.
In a sense, the ideal is deescalation and education rather than punishment
Sometimes a gentle warning as things are getting impolite, and good old moral suasion works. Sometimes I mod message for more serious patterns, and sometimes have to suspend people.
In one case, with an escalating series of events that was intentional trolling... we called in a CM to give an extended suspension.
And let me say, I hate suspending people in most situations. Its necessary some times.
There's no red line that goes "this is when someone gets suspended" - We look at context, and the people involved. Try to see if there's any subtext or if the user has any history of doing it. In some cases, I've even recognised someone's distinct writing style when he generated a new account.
So, if you've been provoked, and we go "Guys, play nice" and everyone involved deals with it like a grownup, we don't need to suspend. I've even poked my nose into a site where I don't moderate, but I know the mods well and went "Hey, this isn't nice" and got the expected response (OP self deleted.). No suspensions were handed out as far as I know, and the individual realises folk don't tolerate it as a community.
Lets not forget that suspensions are designed to address an overall pattern of poor behaviour and their effect on the community as a whole (least as I understand Jeff's old post on this). If we didn't need to look at the "big picture" - I'm pretty sure someone in SE (or even the community) could automate the whole process.