There are some users who can (or could) collapse any answer they find, since they are authorised to use Trusted Reporting (Quora feature):
If you are not a trusted reporter, but you have an adequately high PeopleRank, you may still be able to collapse an answer.
The answers at Is it possible for a Quora user to have such a high PeopleRank that their downvote will collapse an answer by a normal user? say that it needs two downvotes. But those answers are from 2011.
Of course, if you keep downvoting answers that someone has already downvoted, and two downvotes are still needed, then you will see immediate collapses. But we don’t know how many downvotes an answer has already accumulated. I have only seen my downvotes collapse an answer intermittently.
This is the theory. Has the collapsing algorithm changed recently? I don’t know, and I don’t know how any one user would confirm it. But given the answers already here, I thought I should provide the status quo ante information here, at least.