How do I remove specific entries from activity stream?

If you want to exclude certain activity entries from your activity stream add the following to your child theme's functions.php file:

function ghostpool_activity_dont_save( $activity_object ) {
    $exclude = array(
        'new_avatar',
        'new_member',
        'friendship_accepted',
        'friendship_created',
        'joined_group',
        'new_blog_comment',
        'bbp_topic_create',
        'bbp_reply_create',
    );
    if ( in_array( $activity_object->type, $exclude ) ) {
        $activity_object->type = false;
    }
    
}
add_action( 'bp_activity_before_save', 'ghostpool_activity_dont_save', 10, 1 );

You can change the type of entries you want to remove from the activity stream by editing the $exclude list.