Additional popup dialogs when completing registration
 

Hi There,
i have got a question to which i am searching around for 2 days now but can't seem to find the required info for.
I run a small scaled forum (11000 members and counting) but as of late i have been getting 'Undesirable users' registering account after account, parking them, acting like utter idiots across my board.
So i decided to have our forum rules displayed when registering to which you have to agree to for starters, but alas, the tick box just takes a scroll down.
The thing i need to do is taking the ;tl - dr; out of the rules shown at registration (that i know how to do) but on several other forums i came across additional dialogs after completing the registration process.
one example i came across was two additional dialogs popping up , the first was 'Are you Sure?' , on checking the box and clicking continue, another would pop up saying 'OK then, don't come `whining if you do get in trouble'

now those additional dialogs i am seeking to add to the registration process, any hints would be appreciated..