There is also an Exit Vehicle keybind in the core WoW keybindings which makes creating a pet bar macro unneeded unless you want to be able to click it. I've been using it since getting my first Tundra then finding out regular dismount did not work.

If you're ever stuck in a vehicle you can also try right clicking it to "Dismiss" it. Stuck meaning no keybinding and no exit vehicle button.

Edit: I've got two toons copied over to the PTR now. I haven't installed the client yet but hope to in the next day or two and try out Macaroon there.