Pop ups are bad in general.

IMO, the worst are the full page, content-blocking, app install requests that appear on thin-content sites.

It's preposterous.

You've proven that you can't be trusted to present your website content in an acceptable manner, and you want me to install your software?

Instant back button.

At least newsletters support open-standard email "push" rather than the walled-garden-de-jour, after publishers lost their investments in "followers" to filter algorithms.