Rab Judah laid down in the name of Samuel: If a man is particular about his [share in an] ‘erub, his ‘erub is invalid; for what is its name? ‘Amalgamation’.
The term "eruv" means a mixture, an amalgamation. The idea is that everyone in a shared courtyard shares in the preparing and eating the meal. So someone who is obsessed with his own share ruins the sense of what it means to be "eruv."
A nice metaphor for what it means to be part of a community, not a part from the community
Not all agree on the legal aspects, although the ethical one holds:
R. Hanina ruled: His ‘erub is valid though he himself might be called, ‘One of the men of Wardina.’ (a place known for stinginess).
You don't want to get called that!