They comment on & "like" the same posts mere minutes apart. They also share pics & tag each other on notes. One will take the same quiz, add the same app, join the same group or become a fan of something immediately after the other one does. This type of facebooking duo constantly posts on each other's wall & shares inside jokes & obvious intimate understanding of their vague status updates. They may chat with each other on facebook even though they are sitting in the same room & could talk audibly instead.
These people come across as insecure, lame, cheesy & noobish in the ways of facebook. Everyone appreciates the feeling of belonging & being a valued part of their facebook crowd, but tandem facebookers take it too far & ironically alienate themselves to a degree. Tandem facebooking lowers social value even though the duo may find a huge sense of security in navigating facebook together. They may be trying too hard to look active on facebook or be too lazy to cultivate an original presence there while an ideal lies more to the middle of the spectrum.
One of the easiest ways for tandem facebookers to overcome this label & demonstrate independent thought & confidence is to sometimes wait a few hours between posting comments or clicking "like" on the walls of mutual friends.
Person B: "No, wait! Wait at least a couple of hours so people won't see that we're tandem facebooking!"