I would take Luigi out on a proper "bromantic" date.
Picnic on a toadstool, take a drive in a 2-man kart around the Mushroom Kingdom until the sun sets and go dancing at a Mario Party at night.
Just to show Daisy that she's really missing out on a great guy and shouldn't play with his feelings like she's doing now.
She's just stringing him along, waiting for either Mario or something better to come along. That bitch.
Also to show that bigoted Princess Peach that Luigi's a standup guy who makes a fashion statement wearing green and is perfectly fine with his sexuality.
And lastly, to show Mario that Luigi is a great brother and should be appreciated once in a while by letting him shine in the limelight for for once.
Instead of putting him in a haunted house for no reason other than to prove his bravery in a ridiculous setting.
Don't get me wrong, Mario is a great guy.
He can just be a jerk to his brother sometimes which is unnecessary, seeing as how many times Luigi has gotten him out of a pickle.
Luigi, standup guy!