Last night I had plans with Girl Who Won't Be My Girlfriend. She had a final exam in the evening, and said she'd call me when she finished.
I got an email from her in the middle of the day stating that she didn't have her phone, so she'd just come over to my house after she was done. I emailed her back to say that would be perfect (since I wanted to watch the NBA playoffs anyway).
Later in the evening, I logged in to facebook and saw that she'd changed her status to "I think I may get lucky tonight."
Imagine my disappointment when I realized that I forgot to give her the new gate code to my neighborhood, and couldn't call to let her know.