You could start by not being judgemental (Please note I'm not implying that you are!). In history and today today, there are people running around with theories that seem crazy ("Jesus rode dinosaurs!", "The earth is at the center of creation!", "Light travels through the ether!", "We evolved from apes!", "The NSA listens to us all!" (See what I did here?)). In fact, String theory itself was recently called "bogus". Theories with involve government abusing power are called conspiracy theories, theories that focus on the mechanics of the universe are called pseudo science. As seen in the comments already, people developing such theories are easy negatively labeled "crackpots" or other insulting names. While there are people who could be assumed to spit nonsense for a living (example in German) there are also people who genuinely believe what they do is correct. And sometimes such people are somewhat ignorant and can't understand why their idea cannot work or is extreeeeemly unlike to do so (e.g. the person portrayed by the woman in this video).
But one in a thousand times if not less, people with different ideas are right. The most prominent example is Galileo, the most prominent of this century until now would be Snowden in my opinion. But there were many critics of Einstein, "Evolution is only a theory", and the current president of the united states doesn't believe in climate change. But to be fair, the country he rules has made its own steps of ignorance before his presidency. And people believe or don't believe if Jesus was a God sent messiah. I'm kinda expecting a flame war in my comment section by now.
Perhaps more telling is that most of the ideas are unfalsifiable, in the sense that I couldn't think of an experiment that would prove or disprove any of it.
This makes it sound a little bit less "bogus" and more like the typical "Your inability to find a proof doesn't mean there exists none." If I remember correctly, it took a while until relativistic effects could be proven experimentally and the non existence of ether was proven by an experiment that tried to prove it.
However, this line you should give to whoever asked you to give your opinion.
Maybe the nature of reality is mathematically undecidable, so we will never know for sure what is true and what is just a nice approximation. I for once sinceriously believe we will never be able to check the "source code" of the universe.
Your inability to come up with experiments to possibly falsify or prove his theory are no indicators his theory is wrong. The implied poor understanding of quantum physics is more likely an indicator, but on the other hand, Galilei also didn't like the tried and proven methods of the time, and these were "approved by god", a much higher authority.
So tell whoever asks
most of the ideas are unfalsifiable, in the sense that I couldn't think of an experiment that would prove or disprove any of it.
only the vaguest notions of quantum physics and cosmology (no equations, electrons being defined as the antiparticles of protons, cute drawings)
is not meeting an academic standard.
If you are feeling generous and interact with the theory person him/herself, tell the person that most other scientists would probably call his theory "bogus science" (this is where you are trying to be polite), a few would even use discriminatory terms like "crackpot" and that isn't going to change until someone (preferrably he/she) comes up with a scientifically accepted method of falsifying aspects of the theory.
Appendix: Stop calling people crackpots
A few readers seem to believe I'm trying to encourage people who are wrong to go on with their way as long as they believe hard enough. This is not the case. I'm simply stating history proves that someone who may seem to have a crazy idea about things may turn out not to be crazy at all and you have no idea of knowing in advance, you can only say that it is highly improbable. I'm answering OP "state your opinion and if you want to make others feel better, try to make the "bogus" more relative." I'm not encouraging OP to do so or question his motives for doing so, I'm simply answering him his question.
Maybe some are thinking: "Well, earlier they just believed in some magical entity that somehow came into existence and was responsible for everything, but today we have the methods of science! We may make mistake now, but in the long run, our methods will prevail!" In this case you are making the same mistakes as the people back then and your magical entity is called "laws of nature". Nothing is absolute. We are unable to rigorously proof non-existence of most things in reality. A person cannot even rigorously proof that it has an exact amount of money, because that means proving that nowhere in the world there is money the person hid there. Impossible*. So please, stop trampling on those intellectually you deem less intelligent, it is barbaric behavior and not worthy in the presence of scientific endeavor.
'* Nothing is absolute, but doing this would mean something like lifelong and/or earth-wide monitoring.