Unless you have a mutual friend, you and this person will never speak, but you will share several awkward glances. There's a certain silent agreement that, yes, you recognize each other from your 100x100 avatars, but why speak in real life when you can just tweet at each other about the new Kendrick Lamar album the next day?
The next time you communicate on social media, there will be zero acknowledgement that you kinda, sorta met, but there is the shared comfort that this Internet "friend" is, in fact, a real person and not an overweight 42-year-old who masturbates to Selena Gomez pictures with Cheeto-stained fingers. Not that there's anything wrong with that.
In the event that you and this person do speak, be prepared to dickride each other about awesome things that either of you wrote.