This is one of the weirdest things I've seen in a while. The obvious answer to the question O'Reilly asks five times and Weiner dodges with such an utter lack of grace is: the Internal Revenue Service. At one point, he seems to take the bizarre position that no one enforces anti-littering laws. At others, he seems genuinely angry that O'Reilly expects a direct, brief answer to his seemingly simple question.
[By the way, according to this article in Slate, the House bill, for which Weiner obviously voted, actually provided for jail time for violators who refuse to pay the resulting IRS-collected fine/tax/fee. The Senate bill, at least at that time, made not being insured a civil offense, for which the penalty was having $750 a year -- if you refuse to pay -- deducted from whatever money the feds end up owing you (eg., your tax refund).]
I suspect that what we have here is a phenomenon I've mentioned here before. Big government liberals favor any number of policy measures that involve massive applications of coercion. (By "massive" I mean widespread, against many people.) Yet they often don't seem to see their policies as coercive at all. It's the sort of mind set that led to Sen. Harry Reid to claim, weirdly, that paying taxes is voluntary.
Wiener couldn't give a short answer to the question because any truthful short answer would make the new law sound so authoritarian, so pushing-people-around, and not at all the way he feels its true nature to be. Anyway, that's the only explanation I can come up with for this otherwise-very-odd behavior.
Update: Reported here is some amazing news that may offer a better explanation of Weiner's behavior. The actual language of the new law indicates that, though the penalty/tax/fine/fee for noncompliance is to be given to the IRS, that bureau has no authority to actually collect it if you choose not to fork it over -- and apparently neither does anyone else!
This is very good news for the millions of young, healthy people for whom the lavish mandated insurance policies would be a waste of money (especially when companies are forced to insure pre-existing conditions). They can just pile up year after year a theoretical penalty/tax/fine/fee which they will never actually have to pay. But it is terrible news for proponents of the system, which will collapse without rivers of money forced from the hands of those same young and healthy people. In other words, the law itself suffers from the same schizophrenia I above attributed to Weiner, wanting to threaten and to make nice at the same time.
If so, this is a shocking case of legislative incompetence. (See also this.)