And boy was he angry.
What's getting on his nerves is the number of kids around the world living in extreme poverty. He reckons it adds up to millions of young people.
Half the children of Africa haven't even got a school to go to!
So Mr Brown says it's time for people to get really angry with politicians and make them do something about it.
He wants to see them forming groups to make the powers-that-be take action.
All the kids I spoke to at the conference were well impressed with the speech and said they'd be starting their own campaigns to get something done.
Mr Brown reckons people power can really change the world - perhaps we should see if he's right?!
Check out this site for some info: http://www.beatpoverty.org/content.asp