How is Father's Day any more relevant to Hackers than it is to the rest of society? If no more relevant (as I suspect), then reminders such as this seem off-topic for HN.
HN is run by people like you and me. We're smart people and we typically post and up vote things that other hackers will appreciate. I tend to overlook birthdays and holidays when I am dealing with other things, and I appreciate the fact that someone was thoughtful enough to post a reminder for me.
Workaholic instant-noodle-eating late-nighters occasionally need reminders of upcoming calendar events.