How to identify inconsiderate personal space hogs

I hate inconsiderate people who invade my personal space unnecessarily like the woman I sat next to this morning. She kept elbowing me while reading her paper. Let me get this clear though she was crossing the invisible line between the seats.

I ALWAYS stay well within my space and NEVER cross over. I think it is only polite. I need to come up with a system for identifying and avoiding these types of passengers.

First of all there are different types of hogs:

1. The Spreader: you know the type, guys who have to spread their legs as far apart as possible just to show us how butch they are. Look, unless you have a fricken hernia the size of a grapefruit keep you legs together mate.
2. The Blocker: these are the people who try to prevent other people sitting next to them. Some blockers do this by simply sitting in the aisle seat, (although this isnt always a blocking tactic:see my post on getting a seat on the 4:40) but usually blockers use their bags to save a seat for their imaginary friend. Most annoying are the Blocker's who humph and puff when you ask them if they would mind moving their bag.
3. The Chicken Tonight: it's all about the elbows. I dont care if you are reading a tabloid or a broadsheet, dont elbow me. It can be done - it takes some practise but you can read a broadsheet newspaper and stay on your side on the invisible line. Ditto for knitting - Knitting Chickens are the worst because the poking is incessant.

Spreaders, Blockers and Chickens Tonighters are all pretty easy to spot. My favourite way to avoid them is to pick someone reading a novel. They are more likely to be regular travellers with advanced train etiquette.