No good, Poe-tay-TOE??

it's not even that funny. Mother and I were walking out of the main grocery store the other day in Dakar and some guy was following us with a bag of potatoes trying to sell them to us. Mother was like, 'What's he doing?" and I said that he was trying to sell us some potatoes. So hearing that we were speaking English he continuing following us saying, "Po-tay-TOE", which for some reason just cracked me up. I think it was how he pronounced it... because outside of the strong emphasis on the "TO" part, he said each syllable distinctly as almost separate words. So, still walking I asked him, "Po-tay-TOE?" in the same way, and he gets enthusiastic now that he's gotten my attention. "Po-tay TOE!" he says again holding up his bag so I can look deeply into the bag of potatoes. I'm really amused now. "Po-tay-TOE!" I repeat to him, confirming that I see now that he has these potatoes. But he's waiting for me to buy some now... I say in english, "Sorry, no". Oh no! He's crushed, but he hasn't given up. "No good Po-tay TOE??" I can't help myself now, I'm laughing outloud.... but I managed to say, "No, no Good Po-tay-TOE!" Then of course I was repeating, "No good potatoe??" to mother and then burst out laughing. I told her that I was sorry because I knew it wasn't that funny but for some reason it just really cracked me up. She said, Obviously. she wanted to know what he meant by saying "No good potato?" and I said, Well it's not really clear which is another reason why it's funny." He could have meant, "Are the potatoes off?-- no good potato?" or just generally, "Potatoes are not good for me today--no good potato?" Anyway aren't you pleased to hear about the Po-tay-TOE--No good potato??"