One should never get downtrodden when it comes to adjectives, so if you were ever afraid of being the one person in the room who was doltish when it came to adjectives starting with the letter "D," or if you ever get dreary when adjectives come up, just keep reading--no need for drastic measures.
As a rule, "Dis" and "Dys" mean bad or ill, but be careful! That's just the way it usually is with adjectives. If you hear an adjective that starts with one of those, it's probably not a good thing.
A short inventory of some "D" adjectives will show how much people like to discuss the more dolorous, or painful, parts of life:
And if you count the permutation, "Dys," you get even more:
"De" in the beginning of an adjective can have a negative connotation, but of course it doesn't have to. "De" means from or of. It's Latin.
"De" adjectives can go from delusional to demure to dental to deserving, and the prefix only sometimes has a negative connotation. In fact, in "dental" there's an entirely different prefix.
Rather than give you another list of words as examples, since there are far too many, consider the difference between "devalued" and "deserving."
A similar thing happens with "Dy." "Dy," like "Di," is supposed to mean two. Sometimes it does. Since human beings often come in pairs or at least enjoy the illusion of symmetry, it makes sense that the language would have tons of words describing pairs.
Diametric, dichotomous, and divorced all clearly have something to do with two separate things. But how do you explain dinky, diurnal, or direct? Once again, the language presents learners and speakers with words that might mean two but don't necessarily.
It's easy to see why divisional means what it does after learning what "Di" is doing in the word, but that doesn't help anyone figure out what's going on in other adjectives very much.
Prefixes are inherited heirlooms as meanings of words die and new ones are created. They lose their meanings with time and become idols of nostalgia, artifacts hidden within the language to be discovered and expounded upon by the scholar, the archaeologist, the lexicographer.