Intentional phonetic spelling of "Oh my god". If said, it would be fast and all one word "like, ohmigod!" The word prefix 'like' is often placed in front of it. The phrase is used mostly by pre-teen and teenage girls and should in no way be a means of deducing the person's I.Q. - but it pretty much speaks for itself anyway.

lil mad is like big mad but the opposite, you mad but not mad to the extent of pullin somthin