The crontab command has one of the worst UI problems:

1. "crontab -e" lets you edit your crontab file, and "crontab -r" deletes it (without asking). The two keys are next to each other.

2. "crontab" (no arg) reads the contents of the crontab file from stdin and replaces it. When you accidentally hit Ctrl-D after it, your crontab is replaced with an empty file.