rm -i
A way to make Unix behave like Windows*. Used by sissies and people who aren't sensible enough to back up their stuff (and will be sorry they weren't, eventually, after a hardware failure).
No, really. I know it's better safe than sorry, but in the five years I've been using Unix (and quite intensively) I've inadvertedly deleted stuff perhaps a dozen times, and not once files that I couldn't recover or recreate in a matter of minutes.
Of course, there's one relatively useful application of this command: if you have a lot of files and want to delete many, but not all of them, and there's no name pattern to distinguish between the two, then it's quicker to rm -i and say yes or no for each file, instead of typing the names of all those you want to delete. But I don't think that occurs very often...
* It asks confirmation for every file it deletes with this command.