Sniper posting

Sniper posting is when you manage to reply just before someone else, therefore changing the meaning in the argument, or making someone else look stupid.

Pete: Your sister is so delicious
John: No, Andrew's sister is delicious
Andrew: I know, I got a taste of her yesterday
Pete: Nice sniper post, John.

In this example, John is writing his reply while Andrew is writing his, and posting milliseconds before Andrew. This is called sniper posting