Weird R-rating

You also have to remember this was still a year prior to the PG-13 rating being introduced. Which is probably would've been if it existed (and what the other vacation movies were rated). So it was either PG or R.

Translated: Gen Z's way of bagging on movies that were incredibly popular when they were nothing more than sperm in their Dad's dicks..

How is that odd? People in the 1980s were more open minded.

The humor is very much not family friendly and I don’t see anything about the plot that would suggest it would have to be family friendly.

I did see this movie several times on the “family” channel however (quite ironic) and it was edited of course and it was not nearly as funny.

The name "Nation Lampoon" itself was well known at the time as a "R" rated magazine that targeted young men and women. The magazine often had nudity (sometimes drawn, sometimes actual photos of women) and had other adult sexual content mixed with comedy. Kind of a natural progression for those that enjoyed Mad Magazine.

Adults also heard the name "National Lampoon" from Animal House (78) and knew it's wasn't necessary family friendly.

And obviously the censors heard of "National Lampoon" which would explain the (harsh?) "R" rating.

I feel like the early 80s (1980-1985) were the peak for movies with tonal clashes as well as the peak for mainstream movies containing nudity.

It was a time when movies were less regulated than TV in the United States. Now the opposite is true for the U.S.

~~/o/

The script is uneven and thus so is the tone. It doesn't know whether it wants to be a gratuitous comedy or, like you say, a family friendly road movie like Planes Trains and Automobiles.