Shoulder spikes. Switch-blade style. 
You can learn to do this. Two doors down. On your left.
Just past the Ministry of Silly Walks.
Ni!
No it isn’t.
When I volunteered at my kids’ grade school there was another parent there who did this. She got way too close as she talked to me, and when I backed up she moved in. Backed me into a wall a couple of times. Usually I just tried to avoid here when I could and endure when I couldn’t. I don’t know what to tell you, unless you can grab something to hold, a clipboard or something, that would put a little space between you.
Would it be possible to come up with an imaginary former coworker to tell them about, one who always got waaay too close to you when talking? Or would they just not hear you at all?
My current manager used to be a close talker. He’d start about a step or two away from you and just kinda inch closer and closer to you. Fortunately, he cleaned his nostrils on a regular basis 
As you can imagine, this made everyone pretty uncomfortable. Finally, one day I asked if I could talk to him privately for a minute.
I said “I don’t know if you realize this, but you get a little bit close to people when you’re talking to them. I hope you don’t take offense at this, we think you’re a great guy. But it’s a little intimidating when someone is right here <waves hand right in front of face>.”
He was a little embarrassed, and started to apologize. I said “it’s no big deal, I just wanted to mention it. You’re pretty buffed (he is too, he’s a short guy but he’s got some muscles on his muscles), and it’s kinda aggressive to some people”. (laughed a little to show it’s not a huge deal)
He laughed and said “ok, I’ll work on it”, and he did.
No problems since.
Has a similar experience with a supervisor that had breath that could blister paint. People were talking about it, and I eventually went up to him and offered him a breath mint. No thanks, he said. “Really, I insist” I said, and laughed. He looked a little startled and asked “is it that bad?”, I shrugged sheepishly and nodded (still smiling). He got the message and got his own Altoids tin.
I’d rather people tell me (preferably in a nice way) about my bad habits that make them uncomfortable, than to have them talk about it behind my back.
Fan your hand in front of your face and say, “Wow! Did you just eat garlic or something?”.
Smile really, really huge–all your teeth showing–and nod frenetically in response to anything they say.
The downside of this is that you look slightly crazy, but you’re probably used to this right now.
ducks
I worked at a bookstore many years back and one evening I was out stocking shelves when there was a female voice behind me asking where to find some section of books. I turned around to find myself face to face with a very good looking girl about my age. If she had been standing an inch closer we would have officially been making out. In the time it took me to tamp the hormone rush down I realized that her accent had her coming from one of the European countries where one’s personal space is a lot closer than here in the puritanical US.
So I directed her to the appropriate aisle and wrote that up as a good day at work.