Once upon a time in elementary school, a student learned how to translate certain English words into math. For example, 'and' usually means 'plus' such as "If John has 3 oranges AND 5 apples, how many pieces of fruit does he have?" means to do $3 + 5$. Similarly, 'of' usually means 'multiply' such as "... two groups of 12 things.." or "... a third of 9" indicate $2\times12$ and $1/3 \times 9$ respectively.
Now foward a handful of years and this student finds himself in my algebra course, where I introduce function notation $f(x)$ and state that this is custmarily spoken as "f of x" but caution that even though we write the two symbols side-by-side, that this notation is supposed to suggest action by the function, and not multiplication, unlike $5(x)$ which does mean $5$ times $x$.
The student raises his hand and points out the obvious duplicity of this nefarious two-letter preposition. I mumble something about how mathematics is famous for abuse of the notations it invents, and move on.
How would you have responded to the student?