Why do we grownups act so stupid sometimes?

I am 16 now... but I remember in 2015 when I was 14-15 yr old I tried to love a 17 yr old girl and used to follow her which angered her bf of same age and he started threatening me by texting me online that he will show me hell on monday... I told him please dont hit I wont be near her again bit he said that he wanted to beat me up first... he even made up stories to his friends who were 16-18 yr olds that I wanted to sleep with her so all of them started chasing and threatened me badly... omg I was really in a big trouble... I dont think small kids will ever do these things like me so they almost never fall in troubles like this