Can I leave tap water to stand outside in order for the fluorine and other baddies in tap water to evaporate?
Could I boil it for the same result?
I'm going to go against the grain here, and say NO. I don't know what the lowest TDS of the water in your area is (average is 350ppm -- http://www.tdsmeter.com/education?id=0018), but 350ppm is entirely too high for VFTs.
A VFT requires 50ppm or lower of TDS (http://venusflytrap.info/gloss-tds.html). If your water is above this, regardless of chlorine or fluoride, you are going to kill the plant after awhile.
This is where the recommendation for distilled, RO, or rainwater comes from. Those sources have very low amounts of dissolved solids.
No and no, unfortunately. Chlorine will boil out in a few hours but fluoride needs a carbon filter. There are other dissolved salts in most tap water that are fine for consumption but not good for a venus fly trap. If your filtration plant uses chloramine you could boil the water all day and there would still be a detectable level of chloramine in the water.
Try a carbon filter with silver to remove most of the problems.
I'm assuming by "baddies" you mean intentionally added chemicals such as chlorine. Boiling it - or just leaving it out for a day or so - will remove/reduce the chlorine content of water but I don't think it does anything for the fluoride content. There are some filtration methods that can be used to remove fluoride but I'm not sure it's worthwhile to do that or necessary.
I'd suggest just setting the pitcher out for a day and it should be fine.
Based on the complete change of the question - from a general one about chemicals in water to one about the watering of a Venus Fly Trap - and the comments (and down-votes), I'd like to follow up with this opinion on the issue:
If your locality is using Chlorine (not Chloramine), it can be remove/reduced (as I stated above) by setting it out or boiling it.
Boiling isn't an effective method to remove Chloramines from the water. There are filtration systems that can be used to help this process. Apparently this is important for VFT plants (and probably others like it) but is considerably LESS of an issue for other plants - indoor plants in offices I've worked at have been watered for YEARS on treated "city" water and done quite well.
For systems using aquaculture or for fish tanks, Chloramine needs to be addressed as it is harmful to the fish but for most plants, at least according to the data I've looked at by the EPA and my locality, the Chloramine-treated water isn't a problem. Personally, this isn't an issue as we're on a well but folks should do research themselves.
There was another question like this here: Chlorine vs Chloramine: Both harmful?