As some of the other answers have eluded to, there are two basic problems with your question:
The first is the question of how you generalize a "tritone" in a non-12-TET based system. One possibility is to interpret it literally as three whole tones (which then begs the question as to how you define a whole tone in a non 12-tone system). Another possibility would be to define it as a half an octave, which still leaves tritones undefined for odd n. Because tritones are inherently defined around a diatonic system consisting of whole tones and half tones, it is not clear what the proper generalization to other systems should be. For example, perhaps with an odd n, you could define the two intervals on either side of n/2 as a minor tritone and a major tritone (bothe of which would likely be dissonant). But to my knowledge, this isn't standard terminology.
The second issue is with your assertion that the tritone is the most dissonant. This is not necessarily true, as we'll see below, and depends on how you define dissonance.
It's not really worth trying to argue around the semantics of an undefined tritone (besides, what about other dissonant intervals, or intervals in non-ET systems?). As a result, I will generalize your question to the following:
Is there an explanation why any interval seems so dissonant in any tuning system?
When formulated in this manner, the question merges into the following question which already has an excellent answer: Is there a way to measure the consonance or dissonance of a chord? (although the title says "chord", much of the answer is concerned with the consonance/dissonance of intervals).
To summarize the answer from that page, two pure frequencies will produce a "roughness" (caused by the interference of the two sound waves) which gradually increases as the frequencies get closer together, and is maximal somewhere around a minor 2nd. Frequencies much closer than that start to be perceived as out of tune versions of the same frequency, and the perceived roughness rapidly decreases until it reaches zero when they are in unison.
However, most instruments do not produce a single pure frequency, but create a harmonic series of frequencies. In order to compute the dissonance of two notes, you have to sum all the "roughness" between all the pairs of frequencies in the two instruments spectra. In this approach, the tritone is primarily dissonant because it is a m2 away from the second overtone of the fundamental (a P5), and inversely, it's second overtone (a P5) is a m2 away from the fundamental.
When you plot this out for all frequencies, you get what is called a Plomp-Levelt curve which looks like the following, though it will probably differ depending on how you weight the formulas, and what the individual spectra of the instruments look like. You'll notice in this graph that, while the tritone isn't the most dissonant interval (at least according to this mathematical model of dissonance) it is the most dissonant interval between a m3 and a m7. Furthermore, the local maximum is actually pitched slightly higher than a tritone (somewhere between a tritone and a fifth). You'll also note that the axis across the top is equally divided into 12 parts from unison to octave. For any other system, you would merely divide the axis into a different number of subdivisions. Or, for other non-equal tuning systems, you would just find the corresponding subdivisions.
Addendum - Timbres and Tuning
Because the above curve that models the degree of consonance for various intervals is determined, in part, by the location of an instrument's overtones, this suggests that instruments with inharmonic overtones (such as xylophones, bells, or synthesizers) might be able produce curves with consonances at different locations, including locations more suited for alternate tuning systems. Sethares has performed some research in this area, and in the linked article, provides a series of timbres theoretically suitable for 10-TET -- including a consonant tritone! Unfortunately, I don't see an audio sample provided.
Addendum - Defining Dissonance
You ask specifically about a uniquely "most dissonant" note, but such a thing does not exist, either at the tritone, or at any other interval. Such a question assumes the existence of a single, objective, quantitative scale by which dissonance can be measured. There is no such scale. There are many factors that come into play: acoustics/physics, biomechanics, neurophysics, and -- importantly -- ethnocultural experiences. The Plomp-Levelt curve provided above is merely one model that attempts to explain the phenomenon of dissonance, which depends on specific instruments' spectra, and it's inharmonicity, as well as making assumptions about how the ear rounds nearby pitches. As shown above, these parameters can be tweaked to produce different curves. As an example of a different model, here is one based on neural synchronization, which, according to the abstract,
"explore[s] the theory of synchronization properties of ensembles of
coupled neural oscillators to demonstrate why simple frequency ratios
may have achieved a special status and why they are important for
Since there is no single objective quantitative definition of dissonance, there cannot be an objectively "most dissonant" interval.