Can I ask you about the dress code?

ive read there is a 'formal' night on board and we cannot even wear shorts to the dining room?

Is this true?

Seems silly when its hot outside we cant wear shorts when eating.

I dont plan on bringing a tux (dont even own one nor do i want to wear one on vacation) or a suit.

Is this going to be a problem? We dont plan on eating at the specialty restaurants.