...わりに means "for ..." or "considering ..." as in "You look young for your age". So basically the girls is saying "Ha, you're doing an old thing in spite of your チャラい appearance."
This means she believes カツアゲ is an outdated act, and チャラい people do not usually commit カツアゲ. Well, I also think this is a general tendency.
In school dramas/manga, カツアゲ is usually considered as a delinquent action committed by people like this:
This is a stereotype which is typically referred to as 昭和の硬派な不良 (lit. "Hard-faction delinquent of the Showa era") today. They are characterized by stubbornness, dignity, violence, hierarchical relationships and resistance to adults. This type of 硬派な不良 is almost dead now, but the word カツアゲ is still associated with this type of school boys.
Today, the word チャラい refers to the opposite of this, characterized by talkativeness, frivolousness, women-chasing, opportunism, sensitivity to fashion/music, and fast-living attitudes. The antonym for 硬派 was 軟派, but it came to mean "to pick up a girl", and today チャラい (i-adjective) has become widespread. (Of course the actual appearance of 軟派/チャラい people will vary from time to time; no one looked like Fujimori Shingo 40 years ago.) While チャラい people may be generally considered by many to be superficial and lacking patience, they seldom take a risk and resort to brute force.