Ztarg
Gratz spelled backwards. Typically used in MMOs
<SoandSo> has earned the achievement Grand Master in Turd Burgling
<You> Ztarg
<SoandSo> xxanht
<You> Ztarg
<SoandSo> xxanht
Ztarg
When the word gratz become too cliche and people grow tired of it, especially in MMORPG's when feats/achievements are announced, you can say "ztarg" in its place.
Person1: Ding!/I just gained a new level!
Person2: Gratz!
Person3: Gratz!
Original Person1: Ztarg!
Person2: Gratz!
Person3: Gratz!
Original Person1: Ztarg!