There is a reason why D Brown is not called a "clown", and it is a good one. All three players you (aptly) cite, D Brown, Monfils and Kyrgios, are indeed the ones who most play "trick shots", but they do it all their own way. I agree with you that to call a player a "clown" is something which is debatable, but one way or another D Brown is, by far, the last from those three which should be called that. Here is why:
As a preamble (this is not the actual argument), D. Brown is actually much better (at trick shots exclusively) than the other two. Considering that he is a lower ranked player -- so he gets much less coverage -- he still has produced way more "trick shot highlights" than the other two. He has a plethora of different accomplishments on youtube, diving volleys, all kinds of tweeners, delicate pick ups, absurd lobs, no look shots, spinning shots, balls the bounce back to his side of the net, behind the back shots shots with racquet facing the "wrong side", slam dunk smashes, tweener jumping volleys while charging the net(!), hell, he has even a jumping-volley-after-a-shot-sitting-on-the-ground (he slept and fell). There is simply no comparison (strictly regarding these kind of shots).
But the main thing is that all those shots are
actually part of his game plan. He tries them continuously during a match, because his game plan (which is basically charge to net/go for a winner as soon as you can)
forces him to do it. In other words, most of the times that he fires a trick shot, is that because
he needs to. Generally, there are no other "normal" options available. He has to jump for the diving volley, he got wrong footed and cannot turn the whole body in time, etc. In this sense, they are actually
not trick shots. They are last resort shots, the only (or the better) option given the context.
Monfils is completely different. As
@atttomole put, he is basically a defensive player, but with huge, insane athleticism. So, when the situation allows, he can use this athleticism and produce "pure" trick shots -- in the sense that he surely had other safer, more orthodox shots available (that is why he is called, not by me, a "clown").
Kyrgios is again completely different. Trick shots are part of his game plan as well, but with a different purpose: to destabilize the opponent. As Monfils, he usually has other safer and better options available (even if he has extremely quick reflexes, that also help). Just watch any of his matches, specially the ones he wins, and see how effective this approach can be. The guy is really, really smart.
I'd suggest that makes Roger "Heidi."
