Can I do this?

I want to customise the kind of urls that vbseo generates for each of my forums.

At the moment, if I have a forum called Cats and Dogs, vbseo links to that as www.mydomain.com/cats-dogs

I want to make it, for example, www.mydomain.com/hello/pets

The key thing is I don't want to use the same pattern for each forum. Some will have added subdirectories, like the hello example, and some won't. Sometimes different subdirectories.

For example I might have another forum called Parrots and I'd like that to make that one www.mydomain.com/goodbye/birds

Does that make sense? Can I do this?

vBSEO allows you to have forum URLs that are completely different from the forum title. (via Forum Slugs) But afaik, you can't use slash (/) in it. So, for example:

You can configure it to /hello-pets/ and /goodbye-birds/ , but not /hello/pets/ and /goodbye/birds/.

ok, cool. That's a good start anyway.

Are the slugs in the vbseo options? I am just about to upgrade to 3.3.0.

This feature is not available via vbseocp. You'll have to edit vbseo's config file.
See this thread on how to do that:

[How-to] Use vBSEO's Forum Slugs - Custom Sub-Forum URLs