This is incredibly inconsiderate, holy stuff. "You have to have wasted this much of your life to be my friend!!"
except its a good way to test its, except for the friends thing
What i noticed is that the name would be sketchy, their level is very low, and on multiple occasions their profile is private. I also noticed they tend to have the same avatar.
Another thing you can do is just block anyone you don't know. Simple as that. If it seems legit i check the profile for anything that we have in common, such as groups, friends or games. If none of those apply or their profile is private, i block them.