Two things that I can think of:
1) Don't think of chocolate bars as real "food". They're just a nice tasting sugar and fat delivery system. And they're definitely not anyone's friend!
2) The problem is not that chocolate bars are "irresistable". I suspect the problem is that you need to form the permanent habit of taking responsibility for your own health. All these little choices, such as whether or not to eat a chocolate bar, add up to have an overall impact on our body's ability to resist disease and general wear & tear.
Personally, I almost never have sugary treats as a snack when I'm hungry since I sometimes want more and more and find it difficult to stop. So now it's only the rare occasions, such as parties, I'll have them - as dessert after a main meal when I'm no longer hungry. I've found that to be the best way to avoid having "just one more".
The forum's website has some good articles that may be of help:Food CravingsEmotional Eating
This next article has a table that shows how much effort it would be to exercise off a chocolate bar.Treats - Are They Worth It?
How to say "No Thanks", a useful thing to tell yourself as well as other people!No Thanks!
This article lists some of the damage sugar can do:Sugar And Weight Loss