No such functionality is delivered out-of-the-box with Mendix. This does not, however, mean that you can't fulfill your client's requirements.
Disabling right-click functionality is done in JavaScript by capturing relevant events (generally on document/window / onmousedown/onmouseup) and not propagating them. If you are using Mendix 2.4 the easiest way to do this is to create a theme package with a modified index page that contains either the JavaScript code to do this or a SCRIPT tag that references a JavaScript source file containing the code.
If you want an example/proof-of-concept I'll write one for you, so let me know here.
To add the JavaScript code for disabling right-click in an application, edit the index3.html file (after testing it you should put this file in a theme package so the modifications carry over to deployment).
In index3.html, inside the HEAD tag, you should see these lines,
<script type="text/javascript" src="mxclientsystem/dijit/dijit.js"></script>
<script type="text/javascript" src="mxclientsystem/mendix/mendix.js"></script>
Right below these lines, add the following code (which I've adapted from other implementations found on the web and tested in IE, Firefox and Chrome),
<script type="text/javascript">
function disableRightClickIE() {
if (document.all) {
return false;
}
}
function filterRightClick(e) {
if (document.layers||(document.getElementById && !document.all)) {
if (e.which == 2 || e.which == 3) {
return false;
}
}
}
if (document.layers) {
document.captureEvents(Event.MOUSEDOWN);
document.onmousedown = filterRightClick;
} else {
document.onmouseup = filterRightClick;
document.oncontextmenu = disableRightClickIE;
}
document.oncontextmenu = function() { return false; };
</script>
This will prevent the right-click event from propagating (if the conditions are met, the handlers return false) and effectively disable right-click.
You can, of course, also put this code in a JavaScript separate file.
Hope this helps.