So this is exclusively "you" as in hypothetically people in general, right? For example, "You know those times when you brush your teeth and water tastes really cold?" would be translated as "Kender du de gange, når en børster ens tænder og vand smager virkelig kaldt?"
"Pænt" is about how something looks and is sometimes used to express "it was nice of you" when someone does something nice for you. So saying "pænt" in this sentence will make it seem like someone is doing you a favor to think about you and would seem weird given the context of the sentence.
The function of the accent is to show the word is stressed when pronounced, because if "en" is pronounced like the article "en" it would not convey the right meaning.
Take the words "alle" and "allé". The accent tells me that "allé" means "avenue" not "all".