If Rick was deep enough in his relationship with Debbie to propose to her then one would think that his freewheeling days had been over for quite some time. The reaction of Rick's friends to his news made it seem like he was still carousing and womanizing with them every night. This suggests that Rick still had not yet let that life go which is inconsistent with his goofy but well-meaning image.
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To me, the purpose of comedy is to point out everyday truths, but in an over-the-top manner, not necessarily going for realism while still driving the point home. Everybody has idiotic or immature friends that stay stuck in in their high school or college lifestyles way too long, often refusing to grow up.
There wouldn't be a movie without Rick's idiot friends. He's the hero, so he's not going to cheat on her, but he still needs his connection to his "old" bachelor life to have that one last ridiculous send-off party.
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wait for iiiiit...
Ah yes, but have you endeavored to probe the Shakespearean elements of the film? Personally, I think there is the self-sacrifice of Hamlet in Rick's performance. However, contrarily, my spouse is of the firm belief that there are parts of Chekov and Ibsen incorporated into the, shall I say, mise-en-scene between Rick and the donkey. I find that far to Kafkaesque for my liking.
I want the doctor to take your picture so I can look at you from inside as well.