Douilles and Couilles, I pronounce them both the same with the exception of the consanant but I am never understood, always a long explanation before I can make myself understood.
I think it is as much a problem for the French listener, some just cant seem to make the mental leap that a word may just be pronounced slightly differently by a foreigner or perhaps using the wrong gender, this despite the fact that they are all capable of a passable imitation of an Englishman speaking French.
Its the failure to understand a word with the wrong prefix (whats the gramatical term, article? pronoun?) le instead of la or recto verso, OK a few words have both forms but given that I probably get it wrong on at least 15% of the nouns I use is it really beyond someones capability to understand?
I think its a bloke thing, sometimes I feel like a sullen Kevin type teenager when people (always men) ask their partner, "qu'est ce qu'il a dit"? the partner usually female who has the ability to listen always knows what I have said.
I find that I have to lip read more and more especially when there is backround noise or music, the people I find hardest to understand in French are usually the timid ones of both sexes, they whisper, often hiding their lips and expression behind their hands or will look away when talking and not make eye contact, and then there are the marmonneurs who make an art form out of not enunciating their words, some of them would make great ventriloquists.
In my diving club I know probably 40 people, there are about 4 that I either really cant understand or have real problems with, one has no teeth, one has a speech impediment, one finds it impossible to look at me directly and prefers to talk to me when he is walking away and one sounds like that halfwit character in the wacky races.
The rest of them in general are so softly spoken in public that when we adjourn to our bureau, the only bar in town that if we are lucky may still be open at 9.30 pm, I cannot hear them due to the television being on despite no-one watching it, I reckon I do well to follow the subject and hear about 15% of what is being said.