To express great satisfaction with someone; to praise them. For example:
Poster A: "Hey guys, I just scripted a shmup where the PC is ZUN and you have to fight the Extra bosses of every game he ever made. The graphics are sharp and the music is originally composed by a friend of mine who owns a studio. Also, it runs on every conceivable operating system. You can download it for free if you want."
Poster B: ":boobtears:"