Word or sentence describing one who presents no facts or supporting arguments in a debate

There are a number of ways to describe a person who refutes claims or makes assertions without presenting a valid argument, but I don't know of a single word to describe such a person. Examples of people employing tactics similar to those which you've described generally fall within the realm of logical fallacies. Logical fallacies are arguments which might appear at face value to have merit, but actually have no merit, due to the fact that they employ bad logic or faulty assumptions.

Some examples of popularly employed logical fallacies include:

argumentum ad hominem - a personal attack on the person making an argument rather than attacking the argument itself. For example, if someone stated "Crime is on the rise", and someone responded with "No, it's not, because you're a stupid face!", that would qualify as argumentum ad homimem.

argumentum ad temperantiam - also known as "argument to moderation" - an argument which presumes (fallaciously) that the truth can always be found in compromising between two opposite positions.

appeal to ridicule - an attack which presents an opponent's argument as absurd without presenting any evidence to refute it. This is not to be confused with reductio ad absurdum which is a legitimate form of argument.

In your case, the person replying "You are so wrong, it's funny!" appears to be employing appeal to ridicule in place of a legitimate argument.

Please note, however, that bringing this to their attention is unlikely to convince them to present a real argument, and will likely provoke a series of ad hominem attacks.

I would say, Thanks, but where's the beef (or meat)?

: where is the content or substance, as in That was a very articulate speech, but where's the beef? This usage was originally the slogan for a television commercial for a hamburger chain attacking the poor quality of rival chains. (1984) The phrase was almost immediately transferred to other kinds of substance, especially in politics. The American Heritage® Dictionary of Idioms

Another nice expression is, all (or lots of) potatoes but no meat.

meat and potatoes: fundamental part or parts of something, as in This paragraph is the meat and potatoes of the contract. This metaphoric term transfers what some regard as basic fare to the basics of an issue. [Mid-1900s] The American Heritage® Dictionary of Idioms

It was really pretty dull and I could not get through it. Lots of talk but no action. It was like she put in a lot of words just to fill up the pages; all potatoes but no meat (Amazon review)