My interpretation would be as follows:
Nah = I don’t agree …
Umm = Uh oh, wait a minute! I haven’t got the mental agility to think that quick, so give me a moment to find something appropriate to say …
Eh = Complete stop of all cognitive processes …
Ugh = Geeze, I don’t like that sh1t …
Pepe = A central defender at Real Madrid (had to look it up although I would bet that’s not what you were looking for)

1. No way!
2. I’m thinking about it.
3. If it has a question, like “Eh?” That means “What?”
4. Ugh means not good. Ugly.
5. Pepe, that’s a person’s name. Pepe Le Pew, that’s a cartoon character’s name. He’s French!

No.
Thinking.
Still thinking.
Not pleased.
Unsure.

Nah = no.
Umm = maybe
eh = unsure or don’t understand
ugh = gross/disgusting
pepe = let’s go get pizza at Pepe’s!

1. I don’t agree and I’m not interested enough to elaborate.
2. Give me a minute, I’m thinking how to lie my way out of this.
3. I don’t care either way.
4. You’re stupid to like that
5. Tinkle