For me I really don’t like the letter “Z” I just feel like having a name beginning with “Z” ends up being a choppy name and I really don’t like the letter anyway. I really hate [name_m]Zayden[/name_m] and [name_u]Zen[/name_u]!
Which letter(s) do you hate?
F, G, H, W, K and P. There are a few names that begin with one of these that I like or even love, but I generally hate these letters.
G and E. I love [name_m]Elijah[/name_m] for a boy, but that’s the only E name I can stand. I also don’t really like O and H.
I don’t hate, or even dislike, any particular letters but:
K - because it feels too Kardashian at the minute
X - because of pronounciation issues
I don’t like F starting a name, it just sounds odd to me, although I don’t mind it ending a name (I have [name_m]Leif[/name_m] on my list) I also don’t like S or B, for no particular reason.
My own name starts with K, but I generally don’t like it on other people’s names. I think the same-letter alliteration between my first and last name makes it ok for me.
Names starting in X just because of pronunciation issues as a PP said… i.e. [name_m]Xavier[/name_m]. Zay-vee-er or Ex-zay-vee-er??
I don’t like any names starting with I, P, or Q but it’s not that I dislike the letter, there just aren’t many names to my taste that start with them.
I don’t like Br to start or anywhere in A name. I don’t mind the k or hard c at the beginning but not a fan of it ending or even in the middle. For example [name_m]Breccan[/name_m] is the worst name imagineable.
I guess I generally don’t like q, w, x, y, or z. I also don’t know many names I like that start with B, although I wouldn’t say I dislike the letter. With P, it depends. I like [name_f]Penelope[/name_f], [name_f]Poppy[/name_f], and [name_m]Phineas[/name_m], but most P names aren’t really my style.
I don’t like Y, Z, Q, X, K, E, or J.
I don’t care for the letter “z” to begin a name. Similiarly I think “x” can be very awkward as well. I think in theory they can be ok, if that’s your style, but in RL, it just seems to be cumbersome and awkward. I have a cousin who just had a little girl they named [name_f]Zoe[/name_f]. Its a well known name so there’s no pronunciation issues…it’s just that those three little letters seem so…uncomfortable. Personal preference, I guess. 
I tend not to like G, F, Q, U, K, or R.
I don’t feel like I hate or even dislike a specific letter, but I find myself most uninterested in B and in M names.
K - I dislike when K is used as the first letter for names that could just as easily be spelled with a C.
B - Generally uninterested in B names.
Q - [name_m]Don[/name_m]'t like this letter.
X - [name_m]Just[/name_m] don’t like it.
M - Typically don’t like names starting with this letter.
G - ^
X, Y and U
K, D, V, P, O, T. There are a few exceptions obviously, but mostly these letters are just ugly looking.