You really to be friends on Untappd with your best friend in real-life, but both of you have "Pending" on their profile page. What gives?
Note: This is very important: the following must be completed on the Web, via a Browser - not the app on your Phone. We're planning on fixing this problem in the future, but for now to get this working, you must do this on the web.
Sadly, one of you have rejected the friendship - which is a total bummer. The good news it can be fix easily. Please note that it's not possible to do this via the app, only the web. The person who rejected it (usually not the one who requested it), need to go to http://untappd.com/user/USERNAME (where USERNAME is the person you rejected) and then click the Confirm Friendship method. Not sure what their username or your username is? Read this: http://help.untappd.com/support/solutions/articles/25000001928-how-can-i-find-out-my-username-
This can to be done on the web / tablet:
Or the mobile web (where this no Confirm Icon - just the Yellow +)
If you see grey on the web or mobile (as shown below), it means that the other person has rejected your request and they need to follow the steps above.