I was curious to see how something like this could "trash an installation".
It seems like the issue is that the Skype installation maintains a chat history. If this poison string is in your chat history, something crashes the client (presumably a procedure intended to linkify URLs in chat).
You can delete your chat history, but it is synced from the server on startup, at which point the client crashes again. That's why your only option is to downgrade to a version without the bug.
Skype stores chat history in an SQLite database located at %AppData%\Skype\[Skype Username]\main.db, as far as I know it is not removed when Skype is uninstalled. You may be able to remove main.db by hand, and hope that Skype have configured their servers to flush the string from chat histories.
It seems like the issue is that the Skype installation maintains a chat history. If this poison string is in your chat history, something crashes the client (presumably a procedure intended to linkify URLs in chat).
You can delete your chat history, but it is synced from the server on startup, at which point the client crashes again. That's why your only option is to downgrade to a version without the bug.