Fenris takes everything Merrill says in the worst way possible; he makes it clear he doesn't like her for three entire Acts.
However, trying to say that Merrill has a sense of superiority over others is incredibly disingenuous of you. Merrill is also the person who tells Fenris that the plight of the Kirkwall elves matter, she's one of the people who thinks that Kelder should die to protect the children from a serial killer, and she befriends people living in the Alienage - which is why she suggests that Sebastian should name his bow after a cranky woman she knows in the Alienage, and why she reassures Nyssa that Hawke and her are there to help.
Meanwhile, Fenris lives alone in his comfy mansion, doesn't want to help others unless Hawke orders it, constantly looks down his nose at other elves--in fact, in Gaider's Short Story, Fenris mentally sneers at free elves for "squandering their freedom." City elves for living like "frightened cattle" and Dalish for "grub[ing] in the dirt." That's right, Fenris flat out looks down on all free elves, city and Dalish, and flat out refuses to help other elves when Merrill tries to encourage him to do it.
- Merrill: You never come to the alienage, Fenris.
- Fenris: I don't live in the alienage.
- Merrill: Don't you care about the plight of our people? Not even a little bit?
- Fenris: I don't need to visit the alienage to know what they suffer. I know it better than you.
- Merrill: I've lived there for years! I see it firsthand!
- Fenris: And I lived it.
... And yet, as Merrill points out, she lives there and has been living there for years. She is living it. She hasn't "lived it" passed tense, she "is living it" present tense. She herself is also actually doing something to try to help her people. He just sneers down his nose and refuses to come over or help others just because he used to have it worse, but doesn't anymore. (I'm sure most elves would kill for the chance to say "I lived it" passed tense, not present tense.)
And in case you doubt that, just get a look at his comment in Mark of the Assassin.
- Fenris: You are too willing to involve yourself in the affairs of others, Hawke.
- Fenris: Each time you put yourself at risk. One day you will not be so lucky.
- Hawke: You have a better idea?
- Fenris: Guard what you have. Keep your head low.
And yet, getting involved in the affairs of others is how Hawke got to helping Fenris, and Fenris got to following Hawke, in the first place. Fenris is okay with Hawke getting involved in his affairs, and risking him/herself to help him against Danarius, but not only does Fenris himself not help other people who need assistance the way he was helped when he was in trouble, but he disparages Hawke helping other people despite repeatedly asking for and receiving help from Hawke.
Who's the bigger snob? The girl who says something that can be interpreted as a bit elitist and superior but otherwise spends all her time actually trying to interact and help others, or the guy who sneers down his nose at every elf and refuses to help out or show any empathy or compassion for others?