Your design is bad, is both the best and the worst thing to tell to a designer.

Onur Cobanli explains:
The worst thing to say to a designer is that their design is bad, and the second worst thing to say is why it is bad. These are also of course also the best things to say a designer; see, for designers their work is like their babies, no one wants to hear their baby is ugly; but unlike a baby, designers can actually change their work as much as they please and helping them see what’s wrong with their ugly babies, I mean designs of course, is indeed greatest thing you can do; but just be careful, since designers are egoist and narcissist, when giving advice be careful, you need to sandwich your words; first offer apprise; tell what is great and what you like, then hit with critique, and then again say something nice; this is the design feedback sandwich, it will work.