There are very few things that are safe to vape "in the wild" so to speak they contain substances such as oils and many other things that could be harmful to the lungs.
The few things I know can be used like certain teas, herbs, (perhaps) coffee and actual tobacco flavoring require special preparation and handling in order to be safe for inhalation and it's often complicated and time consuming to do at home.
Flavors created for vaping really are going to be your best bet, and while it's certainly arguable that we don't know every single thing in those flavors ,they have been in use for quite some time (and when certain substances have been tested for in theory harmfulness, most flavor companies will remove those flavors) and that at least gives you a certain baseline for safety.
Just using vanilla in that fashion is 100% guaranteed to lead to a probably undesirable outcome . Oh it kind of makes sense in "theory" but what we inhale is very, very different than what we ingest in other ways.
Good luck and happy flavoring!
Anna