How fast, cheap, and non-destructive do you need the process to be? If you have some patience and can stand to do this over a few days, then this is what you do.

Get yourself some rubber sheets, like this.

https://www.amazon.com/gp/product/B000QD7LYO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It doesn't have to be these very sheets, but the point is you need a firm but soft and sticky rubber material. a cut up bicycle tire may do the job.

Next, make sure that you have very cleanly wiped the lighter and teh chimney of all grease and oil. YOu need friction, and having slick surfaces will only make the job harder and potentially more "explosive".

Once you have the sheets, you want to cut two pieces. One to wrap around the body of the lighter so that you can get a good grip by hand. The other is for the chimney so you can grip it with a pair of pliers.

When you actually pull it apart, you want to "wiggle" as you go. This should help a lot.

The other thing you want to do is pull apart using your back muscles, not your arms. Yes, I know that may sound weird or unusual to some, but the back muscles are far stronger than your puny arms. So fold in your arms like you're doing a "chicken dance". Grip the lighter close to your body so that your arms stay folded in and reduce your temptation to employ the arms.

The other reason to pull apart this way is because if you use your arms, you are more likely to "launch" something away from you as the potential energy you are using to pull the thing apart is suddenly released. If you keep your arms folded and tucked in, the most that happens is you puff out your chest more, but if you're pulling with your arms you are more likely to flail outwards and throw something, possibly ending very poorly.