When you click into 'View my Achievements' when looking at a game, you can compare against a specific friend to see differences in your achievements.

I would very much like a button that operates similarly to the Global Achievements tab, but searches only among my friends. That way, I can see which achievements are commonplace amongst my friends and which ones I could chase and boast about until my friends finally catch up.

Note: I did see a post by LemGambino from 2012, but I think a fresh revision on this idea is worth making a post about.