To dissuade others from commenting on someone's status by posting a distracting reply.
Stacy's Facebook status: "Wow, so messy! It's like Charlie Sheen's been living here."
Emma's reply: "Charlie Sheen is an underrated actor."
Stacy's reply: "You totally just comment-blocked me"
Rushing into an empty coffee shop for the coffee you've been craving and someone that has no idea what they want or has a ridiculous order has managed to squeeze to the counter before you.
When someone wanders into the coffee shop ahead of you, meanders towards the counter at the speed of stupid, and then holds up the line asking for freshly brewed decaf in her go-green mug.