|This page in a nutshell: It's okay to call a spade a spade – to speak plainly – but remember to remain civil, and to stay focused on improving the encyclopedia.|
Although editors who consistently engage in disruptive editing are disruptive editors, and editors who consistently vandalize are vandals, there is still a requirement for editors to be reasonably civil to each other. But being civil should not be confused with being friendly or courteous, let alone charitable or credulous.
It's OK to let others know when you think they're acting inappropriately, but a bit of politeness and tact while doing so will get them to listen more readily. One can be honest and direct about another editor's behaviour or edits without resorting to name-calling or attacks. Discuss troubling edits, in reasonable terms, on that article's discussion page. If the behaviour of a user remains troublesome, use the dispute resolution process. When referring to a particular bad edit, it is always best to include a diff.
A complement to this is Wikipedia:Don't call a spade a spade.