The definition of Seattle’ing someone is making plans with a person or event and saying you’ll definitely make it initially.

A few days (usually 2 or 3) before the event you say “I’m excited. I’ll try to make it!”

Six hours before the event you send a text saying that you will try to swing by.

[Event Happens]

The day after you say “Oh I’m sorry I couldn’t make it.”

(Clearly this does not to apply to every person who lives there and does not exclude people outside of the city, but it is part of the city’s reputation now…that people will say “yes” despite wanting to say “no”)