Euros? What's so funny about it? In episode 4, the girls are running out of toilet paper and decide to go buy some but they don't have enough money so they ask the crew member to donate some of their money. Some girls don't have money, one of them want to use check and one other even want to donate a Zimbabwean currency. But when Mina (she's German) says she only have Euros all other girls start laughing. (around 5:30 mark)

So what's so funny with having Euros?
It's not &quot;Euro&quot; that the girls were surprised about, but how Mina referred to herself.
Here's the script in Japanese:

わしはユーロしかない。
「わし」？
なんかわしの顔についてるか？
「わぁ～し」？あははは！
（皆笑っている）

Here's the literal translation:

I only have Euros.
&quot;I&quot;?
Is there something on my face?
&quot;My&quot;..? Hahaha!
(Everyone is laughing)

Here, Mina used わし (washi), which is the first-person pronoun used commonly for elderly, especially from Edo period.

Usage notes
The term is generally only used by the elderly, and its use is often considered stereotypical of them. As such, it is frequently used in TV shows and comics to emphasize the age of characters.
More commonly spelled 私, or in kana to make the reading explicit.

In anime/manga culture, if spoken by young girls, she can be considered as ロリババア (loli baba, old loli): girls who look young but act old. (But since this is a one-off joke from her, Mina is not)