Smelling it through their skin really resonates...
...but also the way their voices change. Not just the tone and the calculated attempts they make to not slur their words, but the way they enunciate.
I was once on a teleconference when a co-worker who was later fired came on the line completely drunk. I was the only one who noticed. When she did it a second time everybody noticed and I had to have her dropped from the call. We gave her a chance to keep her job and go to rehab on our $$ (because I insisted as the codependant that I am), but she declined so we fired her.
Here's the pathetic/funny part (not funny ha-ha, so don't freak out on me). I was linked to her on Linkedin, and over the months it became clear to me she was getting worse as she had started to go online and drunkenly manipulate her profile and contact people. The spelling and language was getting worse and worse, and for awhile I could only watch like it was a train wreck. It got so bad I finally had to disconnect from her. Very sad.