Given the plethora of orphan suit jackets at thrift stores, if anyone is interested in wearing orphaned jackets, the rule is the pants have to be tailored in the same way as a suit pant. This way the silhouette of the suit is maintained. Chinos instead of khakis (if anyone does not know the difference just do a quick google search); the jeans should not be baggy or low rise; dress pants or orphaned suit pants. Also chose pants whose colour is a stark contrast with the jacket, so it does not look like you are trying to put together a suit. I will not mention that the colours go together. That is a given.
Forgive the noob for having this opinion, I still have not been brainwashed yet. Did I say brainwashed? Sorry, I meant educated.
Speaking of orphans, today I saw a nice orphaned canali suit jacket at a thrift store, but too big for me. Based on its style two buttons, two vents it was not that old. When I was browsing the pant section I found the matching pants and united them. I am sure I made someone very happy today, although he does not know that I am to thank.