What's the Point of Chewing Gum?

Being an American, Donna wants to learn more about the Chinese. She's talking to her Chinese friend, Jeff. (D=Donna; J=Jeff)
D : Hi, Jeff! What's up?
J : Nothing much. What about you?
D : Same as usual. Here, have a stick of gum.
J : No, thanks. I'll stick to my own brand.
D : And what brand's that?
J : Actually it's not gum. I eat raw garlic instead. Want a piece?
D : No way! So that's where the stinky smell is coming from.
J : Hey! Watch your tongue, OK? Garlic kills germs.It's good for you.
D : Says who?
J : Well, according to...
D : Never mind. Please stop talking. Your breath stinks. I'm out of here.
J : Boy! These Americans don't know what's good for them. Besides, what's the point of chewing gum anyway?

身为美国人, 唐娜很想多了解中国人。她正在和她的中国朋友杰夫说话。
唐娜:嗨, 杰夫!近来如何?
杰夫:没什么, 你呢?
唐娜:老样子。喏, 来一片口香糖吧。
杰夫:不, 谢了。我还是用我的老牌子好了。
杰夫:嘿!说话当心点, 好吗?大蒜能杀菌, 对你身体有益。
杰夫:嗯, 根据……
唐娜:算了, 请别再说了。你有口臭, 我走了。
杰夫:天啊!这些美国人真不识货。而且, 嚼口香糖到底有什么意思?