There is no way to know.
1) There is always someone who dislikes everything I say.
2) There is always someone who dislikes anything I say.
In these cases, does the same person dislike everything I say, or do different people dislike different things that I say?
I'd guess that it is more likely that is different people; if it were always the same person, you'd probably name them, but Mike is right that the words alone don't tell us.
Thank you both very much.
a) Someone dislikes everything I say.
b) Someone dislikes everything I say.
c) Someone will dislike everything I say.
d) Someone will dislike everything I say.
Are all of these ambiguous as well?
I think 'a' and 'b' suggest that I have one specific person in mind.
If you wanted to say one particular person without naming them, something like a certain person would do the job better for me.