Biting is good...BUT
The down side is the blood... Not sure about many here but the LAST thing I want to do is get body fluids (blood) into my mouth of many bad guys I've met.
You might win the fight and end up if something worse later.
Just something to keep in mind.
Spitting is a good shocker too. I'm not just talking about hawking a looger in their face either. If you have a drink or something, you can part your lips just a little bit, exhale hard, and blast out a fine spray of mist in a decent CONE.
Now something like Cola, lemonaid and other more acidic drinks WILL sting the eyes. Even just water will force them to close their eyes and give you a few moments to act on them.
The worst is chewing tabacco spit. Just a little of that will blind to and hurts like hell.
Getting down to the gutter aspect of DIRTY tacktics though...
I was attacked in the restroom one time... Standing there taking a leak is a pretty vulnerable postion, even if your trying to look out for trouble. It wasn't too difficult for the bouncers to locate the urine soaked guy that tried to rob me in the club after he ran away.
Longest weapon right
(sorry couldn't resist)