You know those little coloured squares beside names to show the status of someone? You know, Green is Available, White is not, etc.

What does it mean when there is a red slash over it? :x

You've blocked them. Simply put.

Odd. Never blocked this person either. It just occurred today. Completely weirded out but I guess it doesn't matter. I unblocked!

:) Thank you.

Red slash? That means the person is blocked.