This is purely hypothetical, based on an anecdote told on a web design lecture a long time ago.
Most websites nowadays require you to click on a little checkbox that usually says I agree to the Terms of Service when registering on a website, presumably to avoid any liability that may accrue because of your use of the site.
However, some sites allow the user to register without marking this checkbox (in the mentioned anecdote, one website accidentally allowed this simply because the check didn't work in certain web browsers), in which case, to my understanding, the user never actually agreed to the terms.
Should the user proceed to sue the website owners, could he argue that he never agreed with these terms simply by proving that it's possible to register without marking the famous I agree checkbox?