MOST youngsters commit crime and join triad gangs out of fun and heroism, and do not believe they would be prosecuted or put in jail, according to an experienced social worker. Mr Lau Wing, team co-ordinator of Breakthrough Counselling Centre, said more youths were committing crimes today because juvenile delinquency was becoming a ''sub-culture''. ''Juvenile delinquency used to be considered anti-social behaviour which youths adopted to express their discontent against school, family or society. ''But many youngsters nowadays turn delinquents not to thumb their noses at society or anyone, but to express their 'couldn't-care-less' attitude. ''Some of them think stealing or blackmailing is no big deal. Those who commit crimes may be regarded as 'heroes' and earn the respect of peers.'' Mr Lau said many youngsters felt ''brave'' enough to break the law because they knew nothing about the consequences and thought they were too young to be prosecuted and sentenced. He said Forms 1 to 3 students were the most prone to juvenile delinquency and fell prey to triads because they were easily tempted by peers. But he said youngsters should not be blamed entirely as temptations and opportunities were increasing because society was becoming wealthier. He advised teachers and parents to show more care and pay more attention to youngsters in order to help them get rid of the ''couldn't-care-less'' attitude by setting a goal for them. Education on the consequences of breaking the law should be highlighted. Police figures show that there has been a 30 per cent increase in the number of youths caught committing triad-related crimes last year. More than 400 youngsters below 16 were arrested last year for crimes such as gang fights or extortion, while 317 were arrested in 1991. Special crime information forms are now available in 48 secondary schools in Wong Tai Sin and Western District to encourage reporting on triad elements in schools.