Htydjtk

Some people like to exchange common words for unnecessarily technical jargon. For example,

Your friend: I partook in ornithological observation

You: You mean you went birdwatching?

Is there a word for what your friend here is doing?

That is, if you asked your friend to stop _______ing, you would be asking them to stop using convoluted wording for no reason.

EDIT: I'm not referring here to the amount of detail, only to the unnecessary substitution of jargon into an otherwise straightforward sentence.

jargonize

v.intr.
To talk or write jargon
American Heritage
Dictionary

2.(intr)
to talk in jargon
Collins Dictionary

intransitive verb
to speak or write jargon
Merriam-Webster
Dictionary

1.to talk or write jargon or a jargon.
Random House Kernerman Webster's College Dictionary

The definitions I've given are the intransitive versions of the verb, which seems to fit your sentence. These dictionaries all have transitive definitions as well, which go something like:

2.to render as jargon; translate into jargon.
Random House Kernerman Webster's College Dictionary
1 : to make into
jargon
2 : to express in jargon
Merriam-Webster
Dictionary

I would say "jargonize" itself isn't a very common word, so you may be jargonizing in using it, or maybe not, I don't know. Really nothing is done to the word "jargon" other than adding a very familiar suffixal morpheme to it. We do it all the time, often spontaneously.

You can also find the term dejargonize, sometimes hyphenated, though this isn't found in dictionaries. Well, unless you want to include Wiktionary in the count.

dejargonize

1.(transitive) To free from obscure technical language.
Wiktionary

Obfuscate - verb: render obscure, unclear, or unintelligible

This one seems close

There are numerous words that aren't verbs that describe this speech.

Adjectives that come to mind include bombastic, grandiloquent, pompous. Those words can be turned into verbs (bombasticize, grandiloquize, pomp), but as you've said in the comments, in doing so, you yourself would be grandiloquizing.

A plainer request might use a noun form: Enough with the bombast/grandiloquence/pomposity!

I have an adjective. You might ask your friend to "stop being altiloquent".

"adjective Archaic.
(of language) high-flown or pretentious."

I remembered it from the word of the day a couple of weeks ago:

https://www.dictionary.com/e/word-of-the-day/altiloquent-2019-01-20/

You should ask your friend to stop using big words and start speaking ordinary language. Here's how the Merriam-Webster Dictionary defines this expression:

a difficult word used to try to impress someone

Example sentence:

You don't need to use big words to make your point.