A spin of "oh my god" or "oh my gosh" with a z on the end, mostly used by illiterate chicks who type only netspeak and sticky caps.
<girl 1>OmGz K sOoOo i InViEtEd BrEnDoN oVa 2 Mi HiZzOuZe N hE gAwT mEh PrEgGiEzZ!!11
<girl 2>OmGzZz!!1!!!!!!!!!!
<girl 1>i NoOo
<girl 2>u KaNt GeT pReGzZ daT mEeNz U WiLL b FaTt eWwWwwWwz
<girl 1>OmGz!!111 i MuZt AsK mOmMiE 4 a AbOrShUn
variant of OMGTKKYB, or "oh my god they killed kenny!/you bastard!" a sickeningly common set of lines used in the television show South Park after kenny is killed. when the T is replaced with a Y (or a U), it becomes "omg YOU killed kenny, you bastard!"
Use whenever!