diff --git src/bp-activity/bp-activity-functions.php src/bp-activity/bp-activity-functions.php
index 9e5ab42..9fa62a9 100644
--- src/bp-activity/bp-activity-functions.php
+++ src/bp-activity/bp-activity-functions.php
@@ -256,7 +256,12 @@ function bp_activity_get_user_mentionname( $user_id ) {
 		}
 	}
 
-	return $mentionname;
+	/**
+	 * Filters the user "mentionname" used for activity @-mentions.
+	 *
+	 * @since 2.4.0
+	 */
+	return apply_filters( 'bp_activity_get_user_mentionname', $mentionname );
 }
 
 /**