Gmail - A cheeky error message is displayed when attempting to use consecutive periods./via Simon Souris 

Gmail - A cheeky error message is displayed when attempting to use consecutive periods.

/via Simon Souris 

YouTube - An old-school TV static animation is shown whenever a video is unavailable.
/via totoymola

YouTube - An old-school TV static animation is shown whenever a video is unavailable.

/via totoymola

Foodivide - When you try to sign up for their newsletter with the same address twice, they appreciate the enthusiasm./via Shein 

Foodivide - When you try to sign up for their newsletter with the same address twice, they appreciate the enthusiasm.

/via Shein 

Windows Phone 7 - The messaging app icon changes to sad face when an error occurred while sending a message.
/via Wojtek Siudzinski

Windows Phone 7 - The messaging app icon changes to sad face when an error occurred while sending a message.

/via Wojtek Siudzinski

Twitter - On the mobile version, the error message lets you know that typing on a phone stinks.
/via @oi_joris

Twitter - On the mobile version, the error message lets you know that typing on a phone stinks.

/via @oi_joris

IMDb - The 500 error message is based on a movie quote.
/via Factorio.us

IMDb - The 500 error message is based on a movie quote.

/via Factorio.us

Flickr - Error message when you exceed the 140 characters limit when posting a photo on Twitter.
/via Hugo

Flickr - Error message when you exceed the 140 characters limit when posting a photo on Twitter.

/via Hugo

Zappos - After getting a 500 server error, hovering the three main options will make the dog show you what to do.
/via p4ul

Zappos - After getting a 500 server error, hovering the three main options will make the dog show you what to do.

/via p4ul