Hee hee, love this thread.
Yes, a lot of ingredients in haircare products are flammable. Don't light the can of mousse on fire or leave it on a heater by accident.
I've accidentally lit nail polish on fire a few times (while wearing it, I mean, not while it's in the bottle)... but I don't typically use my hair to get a lighter going, so it's not as much of an issue.
What's of more concern is that those ingredients can be quite drying with repeated use...