How can I unambiguously ask for a new user’s "Display Name"?

At a U.S.-based company, I run an intranet system where all new users have to be requested by managers. The "Request New User" form has a single-field Display Name in which I'm hoping for an answer like Bob Jones -- a short but unambiguous name you might use if you were introducing the user at a party.

The overall UX of this registration process is garbage, but largely outside my control -- the form is a template inside a third-party issue tracker. All I can really do is reword the field label, and the small, always-visible help text that appears above the field.

Originally, the field asked for "Full Name" without any further explanation:

Full Name:

Typical Response from Managers: Dr. Robert Vermin Jones III, MD, PhD, Esq.

Because nobody in IT has ever met this user, we can't just mentally correct it. He could refer to himself as Robert, Rob, or Bob. He could go by his middle name. He could go by a nickname. He could be that rare user who insists the system refer to him by his full title when it sends e-mail notifications like Dr. Robert Vermin Jones III, MD, PhD, Esq. says "who left a half-eaten pudding in the fridge?"

After a few of these (and going back and forth with the managers to get the real answer), I had a stab at rewording the prompt.

How should the user's name display on the system? Usually in the form of First Last.

Display Name:

With this wording, nearly all the managers that try to register new people are providing answers that are clearly intended for usernames, such as bjones, either ignoring or completely misunderstanding the help text above the field.

Can anyone suggest an unambiguous wording here? It seems like a trivial, minor thing, but on our end these are annoying to correct (because the manager who filed the ticket invariably doesn't answer their e-mail) and from the user's perspective it looks like one of the first things company IT does after they're hired is get their name wrong.


Edited to add: Annoyingly, this is a low-volume system and new user requests tend to come in batches, so I can't realistically A/B test and it may be a while before I have enough of a sample size to declare victory. I don't mind tracking these down manually, I'm more embarrassed by how unprofessional it makes us look to new hires.