A simple BuddyPress trick to avoid saving activities when members are becoming friends or when a member joins a group.

gistfile1.php

<?php

/* beginning of the code to paste in the functions.php of your active theme */

function imath_activivity_dont_save( $activity_object ) {
	// friendship_created is fired when a member accepts a friend request
	// joined_group is fired when a member joins a group.
	$exclude = array( 'friendship_created', 'joined_group');
	
	// if the activity type is empty, it stops BuddyPress BP_Activity_Activity::save() function
	if( in_array( $activity_object->type, $exclude ) )
		$activity_object->type = false;

}

add_action('bp_activity_before_save', 'imath_activivity_dont_save', 10, 1 );

/* end of the code to paste */

?>