Write down every situation with vomit that scares you. Don't worry about order to start with. So for example:

- me vomiting
- others vomiting
- movies with vomiting scenes
- restaurantes in case I get food poisoning
- chicken - I don't eat any for fear of getting salmonella

These are just examples.

So then you look at that list and write down which scares you the least and what scares you most. So for example it might look like this: Movies with vomit scare me least, me vomiting scares me most. Okay so now you have your least scary thing and your most scary thing. Now put the rest in order in between those two. What scares you a little more than movies, and then a little more than that. Etc etc until you have your hierarchy list.

Does that make sense?