Windowsitter 

Person who lives their life just observing the world from inside their home instead of living it.

That guy is such a windowsitter. He never leaves his house and wonders why he's sad.

Windowsitter by Neamtul August 19, 2022

Window Sitter 

The awkward kids that only sit in the window at lunch in high school. They often have no friends except for a fellow window sitter or two.

That Steven kid is a total window sitter. He has no friends at all I stg.

Window Sitter by thatawkwardhighschoolkid August 15, 2019