Officially, it’s the South Lake Union Streetcar. But in the neighborhood where the new line runs, it’s called the South Lake Union Trolley — or, the S.L.U.T.

At Kapow! Coffee, a shop in the old Cascade neighborhood, 100 T-shirts bearing the words “Ride the S.L.U.T.” sold out in days, and another 100 are on order.

“We’re welcoming the S.L.U.T. into the neighborhood,” said Jerry Johnson, 29, a part-time barista.

Some claim — incorrectly, according to representatives of Vulcan Inc., the company that is developing the area — that South Lake Union Trolley was the original name and that it was changed when officials belatedly realized the acronym.

The $50.5 million project should be completed with streetcars running in December. Underlying the lighthearted opposition, however, is resentment over changes in the old working-class neighborhood.

“There was a meeting with representatives from the city several years ago,” Johnson recalled.

“They asked us, ‘What we could do for you?’ Most people raised their hands and said, ‘Affordable housing,”’ he said. “Then the people from the city huddled together — ‘whisper, whisper, whisper’ — and they said, ‘How about a trolley?”’

Since then, Cascade has been ignored in Vulcan brochures that lump the neighborhood together with Denny Park and Denny Triangle under the term South Lake Union. With the streetcar, said Don Clifton, a Cascade resident, “We learned how fun it is to change the name of things.”