How to type shortcode-like text in WordPress TinyMCE visual editor?

Use a double third brackets then. In visual editor:

[[my-shortcode]]

To show shortcode as a code, in HTML/Text mode:

<code>[[my-shortcode]]</code>

And you can even write anything with a third bracket in this way:

Do something [[once]] and go…

*_{suggested by SergeyBiryukov}