Deleting multiple GIT branches

One thing I always came across, but then never really looked into, was deleting multiple GIT branches at once. Usually this has never been a big necessity, since I never had that many branches to delete in the first place. Since we started work on Colloq, the number of branches has increased a lot and it's a good thing to know to keep the local environment clean.
This resource from Marcelo Luz on how to delete multiple GIT branches is a very helpful one.