Kind of hard to identify a user if there are two completely separate users with different names. According to this user Gilles (moderator on French Language, CompSci and this user Gilles (on Puzzling.SE), the only way to really differentiate from the two is to see the gravatars that hey have picked.
And since you can't tell which Gilles is the one you actually want to ping, how we would we go about this? The latter Gilles apparently insists that having identical names as someone is okay.
So here's my request. Add the gravatar to the names that pop up when you are attempting to tag someone, so that you get the right user. I understand this may be fairly niche, that two users with the same username could be active in the same question, but this can cause issues when trying to ping someone I didn't actually want to ping.
As psubsee2003 points out, the first thing to actually address is choosing a user to ping, THEN adding gravatars to identify the user.