Badly chosen names are practically a correlary to Murphy’s Law; if there is a way a name can get mangled, mispronounced, misinterpreted or otherwise stepped on, the audience is going to find it. Haven’t we all (okay, mostly) had experiences of the sort with our own names in elementary school? Sometimes it’s accidental; emphasis in the wrong place, using the wrong vowel, transposing a couple of syllables. Other times it can be a bit more malicious, as a syllable or two turn into the basis of an insult.
Where are our problems?
First off, long names. They’ll get you every time. The longer a name is, the more likely the person dealing with it is to forget the beginning by the time they reach the end. Or they all start blending together. Either way, in comes the apathy factor, and out goes the audience caring. This goes double when you have similar-sounding long names, as TheZomb points out here.
Consonant clusters and unusual pronunciation characters are also a trap in this regard. The harder a time people have pronouncing something, the more likely it’s going to come out wrong. And the consonants are worse, because when you have too many, “Can I please buy a vowel?” will become a common refrain.
Then there’s what happens if you have both at once. Mark my words, you’ll end up with the bane of every name-maker’s existence: the dreaded Nickname. Falflpaent’kirylisatzr, Dread Lord of the Seven Forbidden Temples, may sound impressive to you, but I give you even odds that he’ll be lucky if the nickname he receives is only Lord Fluffypants. It’s not as bad if you do it on purpose, of course; take Tsynq Yr from Pamela Service’s Stinker From Space. Really, would you not call an alien in a skunk’s body with a name like that Stinker?
Then there are noun phrases. Some people do well with them. I don’t. Yes, Shining Waters or Glorious Bear or Dark Splendor of Oblivion may sound impressive. But it’s very easy to go past these to the point where it just sounds silly and pretentious, and to some people, even the above examples may be too far. Worst is if you go over the line by accident, and you don’t know how to make a smooth recovery. But smooth recoveries are possible, usually by recognizing just how silly this might sound. One of my best GMs had this problem once—he introduced a serious antagonist, Seven Steel Viper, who promptly ran afoul of the entire group snarking on his name in character. Then, near the end of the arc, the group came up against one Bitter Death Ox and—well, in character it was a pause and choke moment. So, having realized that if you can’t lick ‘em, you join ‘em, he created an antagonist who was meant to make the entire group splutter “Where did they get these NAMES?” But honestly, if you’ve got people who can’t respect the things, and you don’t know what you’re doing, do be careful around them.
There you have it. Look at your names carefully, know what traps not to fall into, and you’ll have a far easier time avoiding the character who couldn’t be taken seriously.