Hide some birthdays from the calendar

The calendar should have the option to hide user groups' birthdays (and events) from the calendar. For example, a banned member's birthday should not be displayed.

I'd be happy if it simply honored the "don't show in the directory" group setting, but it would be better if there was a multi-select box in the calendar display birthdays settings where you could select the groups whose birthdays you wanted to hide (or show). If a banned member had scheduled an event, there should be the option to hide that as well.