Why does Starbucks hate the environment?

I was in an airport last week, and it was five in the morning, and I needed a cup of coffee.  Now, slightly because I'm a dirty hippie but mostly because I like pink things, I have a Lilly Pulitzer travel mug.  Rather reasonably, I think, I go to a Starbucks and ask for a coffee in it.

The young lady asks, "Is that a Starbucks mug?"

I, because I have not learned to lie quickly, say, "No."

They cannot give me coffee in my non-Starbucks mug, so I have to get a paper cup.

Really?

I understand places that won't fill your travel mug because it probably has ebola.  I even understand places that won't fill it because they don't know what size it is, and neither do you, because that's a silly thing to know.

But because it's not their mug?  And they had to ask?  Seriously?  I am now even more Starbucks-alienated than I already was.

I am not going to buy their damn mug, because it's hideous and I don't need two.  And next time I might walk even farther across an airport to get other coffee, even if it is stupid o'clock, because, yes, I hate things that much.