Hi, this started to happen very suddenly - I trashed a file and it worked as usual and suddenly everytime I want to trash something else (from my downloads folder) the OS wants my admin password and deletes the file then immediately!

Here's what I did already but it didn't help:
- repaired permissions
- did a "get info" on my downloads folder, gave read&write permissions to my user and applied it to all enclosed items
There also seems to be something weird going on with the permission control - when I do a "get info" on my downloads folder I see "system", "admin" and "everyone" but my user "badidea" is not listed (the user "badidea" is an admin though). When I try to add the user "badidea" to that list nothing happens! I also have a non admin user for testing purpose and when I add that user to the list, the user "badidea" get's added instead!?!?
How can I fix this?