My irresponsible guy got the trait through game bugginess. I didn't have him skip school on purpose, it was that he had 4 other siblings and even though I would send them to school every day, I would get this bug where all or some of the kids would come straight back home after heading to school, which made them all take a hit to their responsibility value every time they "skipped" school . I would still send them back to school but I decided to not have him work towards getting rid of the negative value, just to see what an irresponsible sim would be like as an adult. He was a BUM! :D
I get that bug sometimes when I have multiple sims leaving the lot at the same time. Without fail, some will end up right back at home and I have to keep my eye out for it when playing large households so I can send them back to work/school.
