I very good friend of mine absolutely hates it, she won't let anyone do it even if they beg (and believe me I did)

For her its purely a mental thing, she finds the thought of any face going near something that urinates disgusting (her ex asked her about rimming once, you should have heard the phone call I got after that )

She's not concerned about smell or anything else, and its not like she's never experienced it (and liked it too apparently) she just can't get the idea out of her head

(On a side note: Hubby has always hated doing it, he had an ex who wouldn't give head, so thought "going down on her" might prompt her into being a little more giving. This went on for almost 7 months, he didn't get any head and I think he associates the 2 now so can't do it)