Dude, I went to Jenny's pad last night, and I drank 3 pitchers that afternoon so I had to drop a fat-ass brown bomber in the crapper: when I tried flushing that log down, it was a no-go... I was straight-up flushtrated, homie.
I live in the southeast US. I first started hearing "flustrated" by local speakers a few years ago. It was apparent that the speakers were not using this for comic effect; the speakers were quite angry at the time.
I don't think that it's a combination of flustered and frustrated...just a variant pronounciation of "frustrated". If you look at the examples used by the other contributors on this site, I think that they illustrate the use of this term as "frustrated".