One of my all-time favorites as well. But it's hard to say why. May be because of the scene when Magnum proposes to Vivian a hot dog and then drinks beers with her: just hilarius.
There is a flub in the French version though. When Higgins tells to Magnum the story when he saw Vivian for the second time (in London) he does like Magnum knew the story of the first time Higgins met her.
Can't tell whether this flub exists in the original version since Universal sold the DVDs with no OV...
Another quick note: Higgins is supposed to go to this English shop to get an UK newspaper. In the end, he doesn't take it with him

. There is no flub though, if you look well, the newspaper stays on the table. Just after leaving the shop, he fights these 2 guys. After the fight, he goes with Vivian but forgets on the floor the bag he got from the shop. I tried to see if the bag reappears later on when he takes a tea with Vivian, but nope, no flub.
Just a bad day for JQH! But Vivian did deserve it...