Recently, this started happening:
Shog9 has an immense amount of badges, so many that the number creates a linebreak in the usercard, resulting in weird space below the usercard of the post's author. It also happens when a well-decorated user is the post's author; then the box is just extra tall:
I first noticed it when looking at "The new edit rejection message for "no improvement whatsoever" sounds too hostile." The problem also appears on Stack Overflow:
I'm using Google Chrome 47.0.2526.73 on Windows 8.1 at 1920x1080 at the default zoom level.
Updated 12/26/2015: This is not fixed. It was, momentarily, fixed on Meta Stack Exchange (but not for Jon Skeet's usercard on Stack Overflow), but now the problem is happening again, even at the page I linked above.
After Winter Bash ended (tested 1/5/2016): It's still happening, both here and at Stack Overflow.
Related, maybe: Usernames can overflow the box
Related, definitely, but not a duplicate: Is there enough space in the user card for users who have a very large number of badges?