OptinMonster loads jQuery v1.11.3 by default, use this to remove this function. Useful if the site is already loading a different version of jQuery and the page source is outputting multiple copies. One version for WP users, the other as plain JS.

om-unload-jquery.js

<script type="text/javascript">
  var om_load_jquery = false;
</script>

om-unload-jquery.php

add_action( 'wp_footer', 'tgm_om_attach_pre' );
function tgm_om_attach_pre() {
	?>
	<script type="text/javascript">
		var om_load_jquery = false;
	</script>
	<?php
}