Next time a salesperson (or management) who walks on water starts ranting at you "why did this simple maintenence call take 2 days instead of the one day I gave you" look them straight in the eye and say...."Show Me" Show me how its done. Do not MF the person or swear in any way.
I would add that, assuming you are doing a stellar job, you should welcome these types of incidents as oppurtunities for education of superiors and laterals alike. Because by the time someone has finally 'had enough' of your 'ridiculous' and 'padded' estimates to 'call you out' on it publically, they have already rehearsed their 'rant' a couple times with your/their peers, derogating you at every turn. And so Michael you are correct that this misconception must be debunked.
However, a word of caution is in order, because although I don't doubt how effective the correctly deadpanned 'Missourian Motto' may be, Michael has a very matter-of-fact tone that belies his actual wealth of experience in these matters. Meaning easier said than done. It's as if a different, though equally qualified Michael, advised "When they double-team you, just pump-fake and then fade the 3 over Magic's head. Try it." Because the reality is that you might not know what comes after that 'stern look straight in the eye', and its best not be caught 'flat-footed'. Adding to the unpredictability of conceivable respones would be the presence of others, not uncommon in witch hunts.
So although one may be prepared for the possible retorts of "It's not my job to do yours", (said by peers), and "What do I need you for then?", (said by superiors), I doubt they are heard much. No, what's more likely to occur here, IMO, will be an awkward attempt at justification of the initial aggression, by resorting to the bean-counters favorite device, the dreaded line-item lynching.
Make no mistake, no matter how prepared you are, a public lynching is not easy (Think IRS Audit with Bill Maher as Auditor). If for instance, the inquisitor has in front of them one year of maintenance logs, and begins launching triple-tipped missiles consisting of "date/action/hours" warheads in rapid succession, choosing only the most egregious and deviant looking ones, you'd wish you were at the dentist (even with Bill Maher as the dentist) instead. This is made all the more frustrating by the lack of any specific allegations, e.g. "I'm not saying its wrong, Joe, I'm just asking if it's normal for x to take y long, z times in a row?". You might miss a couple jumpers in your career before you sink any in those situations. So I would say use 'Show Me' only when is absolutely confident of ones work and more of a last resort than a first.
A similar though slightly less confrontational approach might be dubbed "Show You", where you invite the interested party on a service call to have them help streamline the process and get their take on things. If there are inane internal procedures that can be eliminated, its amazing how quickly they can be changed if someone who can change them has to actually follow them. If they demur then they are likely to let it drop.
In a nutshell, when you tell someone 'Show Me' you may create someone who forever will be trying to do just that, although not the way you intend, e.g., "Crappy Cam's Cleaners only take 1hr to clean the crap out of their cams, etc."
'Show You' on the other hand can create an ally and advocate within the firm. Both methods though are based in reality though, the 'Show', so either is morally justifiable, but 'Show You' is easier for us passive aggresive types. ;)