Disallow some tag for BuddyPress activity content

functions.php

<?php
// check if function does not exists
if ( ! function_exists( 'rtmedia_bp_activity_allowed_tags_callback' ) ) {
	function rtmedia_bp_activity_allowed_tags_callback( $activity_allowedtags ) {
		global $activities_template;
		$rtmedia_type = array( 'rtmedia_update', 'rtmedia_like_activity', 'rtmedia_comment_activity' );
		// $activities_template exists and type not like $rtmedia_type.
		if ( is_object( $activities_template ) && isset( $activities_template->activity ) && is_object( $activities_template->activity ) && isset( $activities_template->activity->type ) && ! in_array( $activities_template->activity->type, $rtmedia_type ) ) {
			// check if ul exists.
			if ( isset( $activity_allowedtags['ul'] ) ) {
				unset( $activity_allowedtags['ul'] );
			}

			// check if ul class exists.
			if ( isset( $activity_allowedtags['ul']['class'] ) ) {
				unset( $activity_allowedtags['ul']['class'] );
			}

			// check if li exists.
			if ( isset( $activity_allowedtags['li'] ) ) {
				unset( $activity_allowedtags['li'] );
			}

			// check if li class exists.
			if ( isset( $activity_allowedtags['li']['class'] ) ) {
				unset( $activity_allowedtags['li']['class'] );
			}
		}

		return $activity_allowedtags;
	}
}
add_filter( 'bp_activity_allowed_tags', 'rtmedia_bp_activity_allowed_tags_callback', 1000, 1 );