I've had that a few times, but it's my fault for enunciating too clearly. The minute I slur my words everyone understands. This only refers to a few of the folks who haven't been afforded the opportunity of much education. And it happens more in tourist areas than in non-tourist ones, I think. So it is partly the predisposition of the listener to think in advance that they won't understand & partly my non-verbal behaviour which is signalling my need to get it right. The minute I signal by careless speech that I really am not trying too hard, everyone seems to understand. Course there's also the warn out eardrums factor (loud ghetto blasters). But if you observe 2 Dominican labourers talking one will say something which I understand with no problem & the second one automatically says 'eh?'. So we shouldn't be remotely offended at something people do to each other - many times it isn't gringo specific.