Hi Deion:
It is a very common practice in every day conversation to eliminate letters from words to
hasten a liaison. It is definitely not a regional affectation. For example, mes "peteez" enfants instead of mes petites enfants is pretty typical.
Since the omission of letters in words is more of a manner of conversation than a grammatical issue, there is no rule that would apply to when letters can or should be omitted. It's pretty much up to the speaker, providing of course, that he makes himself understood.
I think the fact that you heard this on You Tube versus seeing it in writing attests to it being strictly verbal. If you saw it in writing, the writer would have to spell it phonetically, e.g. "peteez" instead of petites so that the reader could imagine what is sounds like in his brain.
Hope this helps!