Wikipedia:Put up or shut up

Occasionally in a heated dispute, someone may post on the administrators' noticeboards regarding the conduct of another editor but without providing any evidence (in the form of diffs) to back it up. This is not helpful: negative commentary directed at other editors is hurtful and creates drama at the best of times, and it is sadly all too easy to mischaracterise or outright lie about what another editor did. As such, one should always provide evidence when requested (or ideally to begin with) if one is making such allegations. Otherwise, editors should not expect their allegations to be taken seriously, and indeed may be considered to be acting vindictively.

But "put up or shut up" is rude!
The phrase "put up or shut up" is common enough in the English language to be considered idiomatic. Indeed, in the sense of "take action or be prevented from continuing to participate" it forms part of the code of the United Kingdom's Panel on Takeovers and Mergers. One could coin a euphemism for it which avoids the moderately abrasive "shut up", but the euphemism treadmill suggests that in time said euphemism would be considered just as offensive. Rather than taking umbrage at the use of a common idiom, consider rectifying the problem that put you into that position (namely, that you made a negative comment about another editor's actions without backing it up with evidence).