BuddyPress.org

Try this:

function mohammad_remove_private_message_button( $button ) {
$user_id = bp_loggedin_user_id();

    if ( $user_id == '37' ) // the user ID
	$button = '';

     return $button;
}
add_filter( 'bp_get_send_message_button', 'mohammad_remove_private_message_button', 1 , 1 );

More details here:

[Resolved] how hide tab only for user? not remove/disable