Simmilar to "and then I found five dollars", except with the currency used in the European Union. One would use this phrase to save face at the end of a really bad story with no point.
Person one: So this morning I went to go get a crepe for breakfast but there was a big line so I didn't.
Person two: Oh.
Person one: And then I found five Euros!
The situation in which a pathetic attempt to belittle people is committed, in order to lower the metaphorical playing field to make yourself appear bigger by making reference to past mistakes and embarrassments.
Dickish guy: haha lets post this thing online to make fun of people.
Other dickish guy: Yeah good plan
Victim: This is 70 euros all over again.