Lakota uses infixes
(I'm rusty, but I pretty sure these examples are correct)

In old Lakota (Sioux) to say "I am Lakota" was:

Lamakota yelo.
I/am/friend(ly) (statment, m)

In modern Lakota we've dropped the person infix, made it into a suffix and
the same is now said:

Malakota yelo.
I-am/friend(ly) (Statement).

We used to use the Ma (I) immediately after the first syllable in a verb to
indicate the first person singular, and Lakota is a verb that means, more or
less as a noun, "those considered friend(s)" or "the friendly."
The former infix (now suffix) -ni- (ni-) means "you".  So in Lakota to ask,
"Are you Lakota?" used to be:

Lanikota hwo,
you/are/frind(ly) (formal question)

but is now

Ni-lakota huwo.
you-are/frind(ly) (formal question)

I think most of the Macro-Siouxian languages had a similar system, and that
maybe OmaHa still uses infixes regularly.

A more colloquial AMEnglish example would be the fuc*ing in:

Brandon DW