BuddyPress.org

You can use comments in that fashion however it does leave unnecessary markup in sorce view and the PHP still parsing?

I would tend do remove the whole section using a silly maths expression, something like:

<?php if(1 + 1 == 4): ?>

All of the link from php if(‘activity’

to the
endif; followed by new closing endif

<?php endif;>

One of the others might have a better take on this though.