BuddyPress.org

hi @billmann,

to remove only last activity date from profile header:

function bpfr_core_get_last_activity( $last_activity_date ) {
   if ( empty( $last_activity_date ) )
      // we do nothing
         $last_active = '';
   else
   $last_active = sprintf( $string, bp_core_time_since( $last_activity_date ) );
 }
add_filter( 'bp_core_get_last_activity', 'bpfr_core_get_last_activity' );

To remove all last active instance (profile, group & member directory,…), you simply remove the filter

function bpfr_remove_last_activity_filter() {
    remove_filter( 'bp_core_get_last_activity', $last_active, $last_activity_date, $string );
}
add_filter( 'bp_core_get_last_activity', 'bpfr_remove_last_activity_filter' );

Add to your child-theme functions.php or to bp-custom.php

bp_core_get_last_activity function is in buddypress/bp-core/bp-core-functions.php:1418

Note that site wide activity is not affected by these functions.