The newsletter Verbatim had an article some years ago discussing prefixes,
suffixes, and infixes.

In English we have hundreds of prefixes that modify thousands of words. We also
have hundreds of suffixes that modify additional thousands of words.

In other languages there are hundreds of infixes, where you split a word and
add the infix to modify the word meaning. Many Arabic infix words were included
as examples.

The article ended with the three known English infix words:
in-fucking-credible, un-fucking-believable, and fan-fucking-tastic.