Dealing with swathes of crazy a$$holes, you need to have a firm hand, goes without saying.
Having firm hand is kind of the opposite end of the spectrum from being cordial and approachable.
Thus in some respects, the bigger an a$$hole a dude/woman is, probably lends themselves somewhat better to that job role.
I gotta say though, one thing that really becomes apparent over time, is a "bouncer" or security guard is much more prepared to throw their weight around, when the person they're throwing their weight toward is less physically capable themselves.
As a dorky teenager, security would tell me off all the time for the slightest infractions, and I noticed exactly the same with other dudes my age.
Last time I recall having a slight confrontation with a bottle service gal who was a little wired, I know she actually requested from security to have me ejected from the venue (hurt her pride, nothing more).
The chief of security came about eyeballing me but, honestly figured it was more hassle than it was worth to have me removed (for something he knew was unjustified, but if I was still that dorky kid, I would have been out on my ear so fast I would have got road-rash).
I'm sure we all have upteen stories like that (I know I have dozens more) - so let's hear them?
Just as a brief PS, I'm not saying it's a hard job, or an easy job, but it requires a certain disposition to be effective in that position (which is either predisposed or cultivated, but it's a necessary part of the job) and really, that's what those staff get paid for.