Just tossing your bike on the lawn of whatever house you were at
Whenever we'd bike to a friend's house, we'd basically just drop our bike on the lawn and head inside. It made it super easy to find where your friends were, but if you tried this now chances are you'd never see your bike again.
The whole concept of "spare the rod, spoil the child" was considered a totally reasonable method of discipline. Didn't matter if it was our parents, other family members, or teachers, if we misbehaved or were disrespectful, the punishment was swift and painful.
Drinking and driving
It's not that drinking and driving wasn't illegal, or wasn't terrible, it's that in the days before M.A.D.D. a lot of people didn't see cracking open a beer on the road as a huge problem. Chances are if you got caught, the cops would just make you pour your drink out or pick who they thought was the least drunk to take over driving before sending you on your merry way.
It wasn't that environmentalism didn't exist, just more that most people didn't really care. Plus recycling was only something those dirty hippies did.
Bringing peanut butter in your lunch
There were plenty of kids back then that had peanut allergies, but peanut and other allergy bans just weren't a thing. To make things worse, Epipens didn't hit the market until 1987, so if you had a severe allergy you pretty much just had to hope you wouldn't die.
We all thought they were so cool, and we all totally wanted one at the time. But now if someone told you they had a waterbed, they would honestly seem a little creepy.
Hanging out at shopping malls
If you were a teenager in the '80s then you definitely spent most of your free time just chilling with your friends at the mall. Not shopping, just hanging out. While plenty of kids still go to malls today, if you just sit around for "too long" then they'll start accusing you of loitering.
Basically every high school had these classes, and but only girls could take Home Economics and only guys could take shop classes. Seems especially silly since both teach some pretty important basic life skills, but that's just the way things were.
Violence and nudity in PG movies
The "PG-13" rating didn't exist until 1984, so before that PG movies got away with a lot more. Then Indiana Jones and the Temple of Doom and Gremlins came along and people realized the gap between "PG" and "R" was maybe a little too wide.
Chicken pox parties
Back before chicken pox had a vaccine, most people felt it was best to just get chicken pox out of the way so you wouldn't have to worry about it killing you as an adult. As soon as one kid started showing signs, it was time to gather every child you knew who hadn't gotten it yet for a good ol' fashioned party. Because nothing says "fun time" like exposing young children to infectious diseases.
Fake wood on everything
A hold-over from the 1970s, fake wood paneling was everywhere. On our walls, on our cars, even on our electronics. It was just as hideous then as it is now, but apparently we were blind to it. Some monsters have tried to make it have a comeback, but fortunately, it never seems to last.
Playing outside unsupervised
When we weren't in school, basically our parents would kick us out of the house at the earliest opportunity, and we weren't supposed to come back until either dinner or dark, whichever came first.