This confused me at first but re-reading it i understand. A 'sad-act' is someone who is lame, uncool, who has no friends etc. 'No day's notice' means without giving any day's notice - so you're asking someone to do something the same day. 'Notice' means without warning/asking someone prior to the event happening. So another possible version of the sentence is 'What kind of uncool person would be free to go somewhere on a Saturday without someone warning them there was something else going on first?' which also basically translates to 'I'm cool. If you don't warn me at least a day in advance that you want me to come out with you on Saturday, I will end up planning something else first.'

In this context notice means to inform in advance; to tell, inform, or warn someone of something. "He's prompt about giving us notice of any discrepancy in the accounts."