a pathalogical flirt is someone who flirts without even realizing they're doing so, or they possiblythink that it's all right.
Boyfriend: you were flirting with steve!
Girlfriend: no i was not
Boyfriend: then what do you call grabbing his ass?!
Girlfriend: well that's definately not flirting!!
Boyfriend: whatever, you're such a pathalogical flirt