Name changed because this is potentially outing.
I was at an after-work reception last week. There was mingling. I mingled into a group of four colleagues. All were holding wine. I was holding orange juice.
One of the colleagues - different department, never met him before - asked "Why aren't you drinking?"
I kind of waved my hand, said "Oh, you know, reasons" and laughed. I believe this made it clear I didn't want to discuss the matter without making things awkward.
The guy then said "Intriguing, like what reasons?"
I saw red. I basically listed all the reasons why someone mightn't be drinking alcohol and told him it was inappropriate to ask. I didn't shout or swear and I wasn't overtly aggressive. But my tone was patronising and I took a very forthright kind of stance (unblinking eye contact, standing at full height, no smiles etc.). I didn't give him time to reply, I excused myself from the group and went home shortly afterwards.
Today I got an email from my line manager asking me for a meeting with her and HR people to discuss what went on. Apparently, its a matter of unprofessional behaviour.
I'm not in a union.
I've never had any dealings with HR before. I'd be really grateful to hear anyone's thoughts on this situation. I mean anything - what might happen? What I should do to prepare etc?