The gum-snapper. The heavy-handed perfume-sprayer. The close-talker. Chances are, if you work with one of these "types," he or she drives you completely nuts. It's like how does gum-snapper not know how annoying she is?
But, that's the thing about pet peeves. While most of us are quick to point out the flaws in others, we can be completely unaware of our own. Gum snapper probably has no idea she's driving you crazy because she's too focused on the fact that you CAN'T STOP USING YOUR OUTDOOR VOICE.