Riding a bike on top of the arch of a bridge is something you normally do in video games and then post on YouTube with terrible music behind it. Not in real life. And you certainly don't tell your mom about it.
This bloke is a member of the Stunt Freaks Team, so I guess his family has seen worse. One benefit of owning a GoPro must be that when things go badly — which will happen eventually — at least you (or your friends) end up with valuable frames from the high-def video that can help in analyzing the situation afterwards.
I'm just kidding! This is cool.
I also admit, the Golden Gate would be difficult to do like this.