If I'm going to use my own cup I just bring coffee from home in it.

Personally, when I get a coffee to-go, I want a disposable cup so that I don't have to carry it around for the rest of the day.

To be more effective, all drink prices should be reduced by 10 cents, then a 10 cent surcharge added for every disposable cup. The price remains the same for all customers, but the extra line item reveals the external costs.

Bringing your own cup is also healthier, because paper cup linings are made of plastic that when exposed to hot liquids are likely to turn into microplastics.

My rule is: 1) keep hot stuff away from plastic, and 2) assume everything is/has plastic unless you know for certain.

I wonder how much of it comes down to inconvenience. I've been bringing my own thermos for a year or so now and it took me some time to get used to the ritual of scrubbing it with soap and a bottle brush after use every day - at first I found it inconvenient enough that it made me want to just get paper cups.

Now it's a nice little ritual and I am used to the advantages of bringing my own insulated container with a lid - I can carry it back with groceries or do other errands without worrying about my drink spilling or getting cold.

FWIW I do occasionally see other people at my local coffee shop show up with their own mugs, but I agree that it's quite rare.

I think the habit/friction part is underrated