<?php if ( is_user_logged_in() ) : ?>
<?php if ( !bp_get_activity_is_favorite() ) : ?>
<a href="<?php bp_activity_favorite_link() ?>" class="fav" title="<?php _e( 'Mark as Favorite', 'buddypress' ) ?>"><?php _e( 'Favorite', 'buddypress' ) ?></a>
<?php else : ?>
<a href="<?php bp_activity_unfavorite_link() ?>" class="unfav" title="<?php _e( 'Remove Favorite', 'buddypress' ) ?>"><?php _e( 'Remove Favorite', 'buddypress' ) ?></a>
<?php endif; ?>
<?php endif;?>