You have to pick:

My dog licks my face for a long time whenever she gets the chance - how's this different?

Human mouths are significantly more disgusting than dog mouths.

Who counts as my co-workers? I work in a company with several hundred employees in the building, if they were all to lick me it would take rather a long time.

Joke's on them, I've got a cold right now.

Your immediate co-workers. So the people in your same office, or if that's only you, then your immediate staff. The people you work with often.

I assume this only happens once?

Yeah.