The fact that The S.I.N.N.E.D. System is not only the reverse of The D.E.N.N.I.S. System by name, but in its actual goal:
The D.E.N.N.I.S. System ends with Separate Entirely and begins with the avoidance of going on a date. It’s purely about sex.
The S.I.N.N.E.D. System ends with Do You Want a Tissue? Dennis’ tried and true method to secure a second date, and:
it works for Dee but she sabotages herself—because she has no interest in pursuing a man romantically;
it works for Mac but he bows out—because he already has a man he’s pursuing romantically;
The S.I.N.N.E.D. System is about romance. Dating, consistently, something Dennis makes very clear he doesn't do...
Dennis in Times up- "Well guess what pal, you are ugly and it doesn't matter how much you work out, its never going to change that fact."
Dennis in the its always sunny book published 3 years prior- "Mac for instance is also a 3 in ugly, so even if this exercise we're going to try fails, you'll have some company at your ugly parties. For the record, on the ugly scale charlie is a five, frank is a six, and Dee is a nine."
Dennis considers Mac to be the most attractive of the gang (not counting himself obviously). And I feel like this just further proves what an unreliable narrator he is. In Breaks up he tells mac he has nice biceps and beautiful lips (this is cannon in my heart even though the scene was deleted it still happened). He'd rather cut his limbs off than admit to something like that now.
Dennis has a boner for Macs ripped new body and it makes him so mad how hard he is for him and also so angry and jealous that he's not as ripped as Mac is.
i honest to god have not been able to stop thinking about this scene, this whole moment of mac being like YES!!!! i want to raise a child with you, do you want this with me too? PLEASE? looping his arm around dennis.. he really just wears his heart out on his sleeve even though im sure he knows dennis is nowhere near on the same page as him. to love him so deeply and just yearn for any chance that he can have a domestic life with him. insane. mac mcdonald you are a beacon of light i want you to be happy.
something something shooting a gun together as a metaphor for our powerful but destructive love, something something you figured out the one thing I wanted more than anything else in the entire world and you got it for me and it's perfect