While I don't drink, I wouldn't bat an eyelid at a colleague, client or vendor having a drink with lunch. I work for a company where free beer/wine flows in the office whenever there's cause for celebration, anyway. In fact, there's a few countries where I've worked where I wouldn't be especially shocked about colleagues having a drink with breakfast.

However, a colleague being drunk during the working day? Ah, now that's a different matter.