The use of words such as "clearly", "obviously" etc. in a technical paper Is there any hidden rule for using the words "clearly", "obviously" or similar ones in a technical paper? It can be offensive to the readers in many cases (especially in mathematical proofs), since the reader may not find it "clear" or "obvious". But does that mean that we should completely avoid the use of these words?
Seconding posdef's appraisal, but being a little more blunt: if one is in a position to get away with bullying or intimidating people by implying that it's their problem if one has not explained well enough ... well, I'd say it's still a jerk-y thing to do. If one is in a lower-status position, such words will often be red flags.

Or, coming to functionality versus rhetoric versus "formal proof": at best these words are functionless filler. That is, saying something is clear is not what makes it clear: if it is clear after these words, it was clear before. Conceivably a thing is clear _once_noted_, and thus deserves "Observe that...". But this, too, can be abused if used outside situations where one is noting that something is "a-fortiori" true, that is, is weaker than what the argument has already demonstrated... but presumably suffices for the issues at hand.