A madlad is a dude that did something so incredibly extreme, so fundamentally unbelievable, that everyone just wonders in awe after him. Someone out of their god damned mind who did something that no sane person would have thought possible. It is often preceded by the word “absolute”.

its just an absolute sick cunt that can do literally anything no questions asked. he or she is also usually a nice cunt (don't fuck with a mad lad)

a great dude

An absolute Madman, an absolute savage, pewdiepie has referred to “Dean” as a madlad. This is because “Dean” sat on the floor when he was asked to!

Used ironically for a person who thinks he did something daring/cool/rebellious but didn't.

Someone who is able to do insane things with things holding them back
I.e. Christopher Aka Captain Crip

Some who goes far beond for a joke.

There is a subreddit about them.