I love watching niche ecchi I discover from just looking at freaky gifs of them prior and then genuinely obsessing over the main girl and series as a whole briefly, it's a nice feeling and I like it whenever it happens
I understand why'd you think it's unfunny, For me I feel like sexual jokes are genuinely hit or miss and there's absolutely no in-between they're either peak or ass
In the director's commentary they revealed that this wasn't originally in the movie but that Disney asked them what they would do if they had a budget for a few more minutes and this was what they wanted to do
To them it was like the cherry on top after working on the movie