EDICT-based dictionaries mark the word やじ馬 (野次馬) for "onlookers, street crowd, or rubbernecks" as sensitive.
I cannot find the word in the 放送禁止用語 lists and Wikipedia page also does not seem to mention any particular warnings on usage.
So my question is: is it really sensitive and to what degree?
Would it be offensive against someone who was a member of street gathering? Or would it generally be bad taste to use the word in a semi-official situation, just relating the story "there was an accident and huge crowd gathered"?