Now since I'd always mostly spoke to my friend in Cantonese, this naturally carried over to my interactions with her family. Her sisters were fluent in Cantonese, like her, mostly from watching TV. Her father had spent time in Tangkoáⁿ 東莞 and probably spoke the best Cantonese in the family. Her mother and baby brother were kind of in the 識听唔識講 category, but sometimes they would bust out in Cantonese too. The brother is definitely making progress in Cantonese -- he's about 13, and learning Cantonese is I guess a rite of passage into adulthood for "kids these days" in Teochew. The mother and brother were the two members of the family that tried to use Mandarin with me. For some reason, though, the family came under the impression early on that I didn't speak or understand Mandarin. They knew I was from Taiwan, but it made perfect sense to them for a Taiwanese guy not to speak any Mandarin.

Toward the end of my stay, I fielded a phone call in fluent Mandarin. From then on the mother started talking to me in Mandarin again. I would respond in Canto. The brother more or less talked to me in Mandarin the whole time. I guess it was hard for him to grasp the idea of anybody not being able to speak Mandarin. I talked to him mostly in Canto as well. The father and sisters just talked to me in Canto the whole time.
More on language attitudes. The kids streamed a lot of Hong Kong TV on www.qiyi.com. Qiyi being a pan-China site, a lot of the videos on there are dubbed in Mandarin -- the stiff, fake kind of dubbing that U always get in Chinese countries and Vietnam. Now whenever they clicked into one of these dubbed videos, the sisters would click BACK in disgust and go back to the menu to look for the undubbed Cantonese version.
The family stayed in a part of Kiat'iông called Châkiô 槎桥. Despite the arcane character 槎, châ is actually just the everyday word for WOOD. I usually see it written as 柴 in the Banlamese context. It seems that Banlamese and Teochew have totally different systems of 俗字 sio̍kjī.
At the bus station in Soaⁿthâu (not Soàⁿthâu) = SWATOW, I noticed that all announcements were made in Teochew first, and then Mandarin.
One last observation. Teochew families have a lot of kids. They were having four or five kids all through the '80s and '90s. It's no mistake that Kúiⁿciu and Chimcùn are "overrun" by young Teochews -- there's just so many of them. So the number of Teochew speakers in Tn̂gsoaⁿ is probably a lot higher than what it was "the last time somebody checked."