Learn Spanish (Spain): Para mí, es imposible comerse todas las palomitas. - For me, it is impossible to eat up all the popcorn.

The se attached to the end is the aspectual se. With verbs of consumption like comer (to eat), adding se emphasizes that the food is consumed completely from start to finish. That is why the English translation says "to eat up" rather than just "to eat".

Since the sentence starts with Para mí, shouldn't the verb be comerme?

This is a great catch! Even though you are establishing your own perspective with Para mí, the main grammatical structure here is es imposible (it is impossible), which is impersonal. When an infinitive follows a generic impersonal expression, we leave the pronoun in its default infinitive form (se) instead of changing it to match the speaker (me).

Why do we use Para mí instead of Por mí here?

We use para here because it expresses an opinion or personal perspective, meaning "As for me" or "In my opinion." If you used por mí, it would change the meaning to "because of me" or "on behalf of me," which wouldn't make sense in this sentence.

Why is todas las palomitas plural when "popcorn" is singular in English?

In Spanish, popcorn is treated as a countable noun referring to the individual popped kernels (una palomita is one piece of popcorn). That is why it uses the plural las palomitas and the plural adjective todas, unlike English which treats popcorn as a singular, uncountable mass.