How do I create and delete a forum via POST to taxonomy_term?
Part one: How to delete a forum.

curl -i -X DELETE \
  -H Cookie:SESSe6abeefcafe=ovQpO6ahoQYUUREX23bre_2Q1onya55i9fbmzq7TWEE \
  -H X-CSRF-Token:v6j7r9Rbase62tokenHere-m9YYZA \
  -H Accept:application/json \
  http://myserver/rest/taxonomy_term/7


Some notes:


to construct the URL, you need to use the Term ID of the particular forum you would like to delete
You need to use the Cookie obtained from the prior call to /user/login 
You need to use the CSRF token obtained from that same call




Where does the term ID come from?

The term id in my case, is something I retrieved from a combination of two other calls: one to retrieve the taxonomy id for the forums, then another to retrieve the terms under  that taxonomy. Like this: 

curl -i -X GET \
  -H Cookie:SESSe6abeefcafe=ovQpO6ahoQYUUREX23bre_2Q1onya55i9fbmzq7TWEE \
 'http://myserver/rest/taxonomy_vocabulary?parameters\[machine_name\]=forums' 


The response is like this: 

[{
  "vid": "1",
  "name": "Forums",
  "machine_name": "forums",
  "description": "Forum navigation vocabulary",
  "hierarchy": "0",
  "module": "forum",
  "weight": "-10",
  "uri": "http://myserver/rest/taxonomy_vocabulary/1"
}]


And then, with the taxonomy ID returned there, I can retrieve the terms, which correspond to actual forums, like this: 

curl -i -X GET \
 -H Cookie:SESSe6abeefcafe=ovQpO6ahoQYUUREX23bre_2Q1onya55i9fbmzq7TWEE \
 -H Accept:application/json \
 'http://myserver/rest/taxonomy_term?parameters\[vid\]=1' 


The response is an array of JSON items, each of which has a term id.  You can then choose one of those term id's to delete, as above. 

Part two: How to create a forum.

To create a forum, do the converse; add a new term in the same "forums" vocabulary. like this. 

curl -i -X POST \
  -H Cookie:SESSe6abeefcafe=ovQpO6ahoQYUUREX23bre_2Q1onya55i9fbmzq7TWEE \
  -H X-CSRF-Token:v6j7r9Rbase62tokenHere-m9YYZA \
  -H Accept:application/json \
  -H content-type:application/json \
  http://myserver/rest/taxonomy_term \
  -d '{
    "vid": "1",
    "name": "Another Forum on the site",
    "description": "",
    "format": null,
    "weight": "10"
  }'


The vid property needs to be the "vocabulary id" of the forums
vocabulary. The uuid and the tid of the newly-created term will
be generated for you. Unfortunately, the tid will not be returned
for you to reference. You need to query again to find it.

curl -i -X GET \
  -H Cookie:SESSe6abeefcafe=ovQpO6ahoQYUUREX23bre_2Q1onya55i9fbmzq7TWEE \
  -H Accept:application/json \
  'http://myserver/rest/taxonomy_term?parameters\[name\]=Another+Forum+on+the+site'


Response:

[{
  "tid": "36",
  "vid": "1",
  "name": "Another Forum on the site",
  "description": "",
  "format": null,
  "weight": "10",
  "uuid": "dcbe0118-c160-4556-b0b6-1813241bb851",
  "uri": "http://myserver/rest/taxonomy_term/36"
}]


Therefore, make sure you use unique names for these "terms".