First, what the heck is a “dark pattern”?

'Dark patterns' are flows or design created to mislead users—usually to take an action they didn’t want to take. NNGroup correlates some dark patterns with 'needy patterns' (that's a little nicer as far as intent) and describes them as "desperate attempts to influence user behavior." Sometimes dark patterns are not intentional, but the consequence of not empathizing with users.

You've seen these and likely fallen victim. It's possible you've even built one. I'm not judging you—even I’ve suggested dark patterns to hit goals and immediately regretted it. ‘Doh.