Which font is the most/least unprofessional?

I don't like serif fonts. A hated colleague goes to the trouble of changing our dreary email default, it is Tahoma, into Times New Roman, the silly ****.

Helvetica is nice. Calibri is okay. Absolutely the best, and not just for the name is Akzidenz Grotesk: https://en.wikipedia.org/wiki/Akzidenz-Grotesk

If by non-standard you mean those not available on Microsoft, there are some you can download for free. Open Sans is a favourite of mine, but it's something I saw a website use, found out what font it was and had to download it to be able to use.

Comic Sans makes me shudder. I remember I once saw a book in Waterstone's that had the reviews of other authors in Comic Sans - like ... why would you do that? Why?
I still use it from time to time, but I'm not a big fan of Calibri. It really annoys me that it's the default font for Word - when I go to a Word document, it's almost automatic for me to change the font (I'm usually a Times New Roman, Georgia or sometimes Arial dependant on what I'm writing kind of girl).

Chinese

Comic Sans was good enough for CERN when they announced the Higgs Boson.
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Comic sans is kind of unprofessional but it makes whatever your writing much more nicer to read. Ariel is the pro one but it's boring and so common, that could be the reason why you choose to use it tho

pretty much m8 rofl

Wingdings

thanks for rep

Calbri headings is where it's at
It's just dawned on me, Should it be used for headings because it's my go to... :s

what be wrong with calibri body m8?

It's too wide and short, basically it's just not headings...