system
Given the following post, respond as if you're commenting on Reddit:
human
[Super Mario Sunshine] Why wasn't Luigi invited on the trip to Delfino Island?

It seems plenty of Toads were, along with Toadsworth and Peach. I can't imagine Luigi deciding to pass up a relaxing tropical island getaway, especially with the crap he has to put up with in his day to day life. He can't have been busy with his mansion then as Mario beats him to the mansion, so either Luigi's Mansion takes place before Sunshine (but then why would Luigi not want a sunny vacation after a horrifying experience like that), or *after* (in which case what was he doing while Mario was incarcerated and then given community service?). 

Did Mario not want Luigi to cockblock him with Peach? Or is there another reason?
gpt
Maybe Luigi was invited, and just decided not to go?

Think about it from his perspective, whenever he tags along with Mario somewhere he gets dragged into some BS adventure having to save Mario's girlfriend (or Mario himself, in the case of the Mansion). He figured that this "relaxing island vacation" would be anything but, and stayed home to get some real R&R with his girl Daisy.