Okay, I'll explain it better.
The situation is: you're too lazy to just look through their friendslist. ^^
1. You go to your friendslist
2. Click on... let's say some elitist friend who you haven't talked to for ages and has only 12 friends..
3. Look in the friends in common part.

If you're not there, you know you're not on their friendslist because... you're on your own friendlist and you should be a "friend in common" with them. x]