The split second after you've said something that you really shouldn't have said, and realise that you shouldn't have said it.
an example of the oh-shit! moment = "those jeans make your thighs look fat" ... oh shit...
An Oh my lanta moment happens when some one of the age of 20+ punches a toddler and below.
Oh my gosh Greg why did you punch that newborn this is a real Oh my lanta moment.
When you have been drinking heavily and are having a great time, when suddenly you become extremely nauseous.
I was dancing at the frat party last night when I had an oh no moment and puked all over the pong table.