Signing off as "Salty" instead of "Sally." Including 18 line items in your signature block, including your parents' home number. Forgetting that you already pushed "send" on your daily e-mail to your mom, and closing the subsequent e-mail to your boss with, "Love, Sean XOXO." Realizing that upon sending said e-mail to your boss, you accidentally hit "reply all" and thus also sent your hugs and kisses to your entire team. The ways we can bungle a professional e-mail are endless and there is arguably no worse way than how we sign off.