<?php
    function bphelp_hide_new_topic_button() {
	if ( ! current_user_can( 'edit_others_topics' ) ) {
    ?>
    <style type="text/css">
        a#new-topic-button {
                display: none !important;
        }

    </style>
    <?php
	}
    }
    add_action ('bp_head', 'bphelp_hide_new_topic_button');
    ?>