Fucking love this thread. I have a couple SW blazers I wear all the time in the spring/summer/fall. I'll be back with more pictures that are not of me, but I will say that margiela and dries are my go-to for inspiration:
Dries, one of the only 3-button blazers that I have ever loved - and I love it to bits. Wear it all the time. Unlined cotton.
MMM. Wool, unlined, omega-shoulder
All MMM, shirt is CKC
I will forever regret hemming those pants
MMM Shawl collar wool/mohair DJ
MMM Cotton "travel blazer" - rough 'n tumble cotton, washer/dryer friendly; rumpled, oversized fit
Raf Simons, 2003 - wrinkled wool/cotton/linen (I think)
Raf Simons, 2009 (cotton, elastene)
Burberry, early 1960's (wool, lined, "hand-me-down" from my grandfather)
As you can probably tell, I tend to just wear them with jeans like I would a light jacket. I'm worried I'm going to have to sell all three margiela blazers, though - two are a bit tight and one might be just a bit too big. Generally, I reach for the striped dries whenever it's springtime and I'm feeling saucy, but this is definitely a look I like, so I'll probably just accumulate more as time goes on. I'd love to ape some of the Dries/Margiela suit-with-sneakers looks that Trill and Parker are so good at, too.
I like the oversized look when it's paired with loose trousers, like in the grey DB Dries suit Parker posted. I think Ervell does a great SW+D blazer/suit look too, but I'd be wary to try since I'm not really sure I have the body type for his pieces. Margiela works pretty well on me, but - and I've posted this recently - I'm interested in some of the softer, more Fok-ish Italian brands. I'll have to give some a try, at some point.