Was flying on QR J ex-BOS. Went to BA lounge, denied entry, was told "QR won't pay for your access" (QR contracts AF lounge). As result, no shower before flight (BA is only lounge in that terminal w/shower). However, I thought oneworld policy was any passenger of one airline/program can access any partner lounge when entry criteria is met. In this case, BA lounge lists "business class" for access on oneworld.com BOS page, along with the text "Access for eligible customers traveling on any oneworld member airline.".

Was my denial in accordance with oneworld policy?

BA regularly refuses access to a number of its lounges based upon capacity issues. Oneworld lounge policy allows this.
https://www.oneworld.com/ffp/lounge-access

Also see this post in the BOS lounge thread in the BA forum:
http://www.flyertalk.com/forum/28452522-post132.html

They were willing to let me in if I had OWS (I didn't), so it was not a crowd issue. The issue, as they explained to me candidly, was they're not gonna get paid by QR for my usage. With OWS, presumably they could charge the program that issued the status.

Maybe the problem is QR doesn't want to pay. Are they allowed to do that?

QR uses the AF Lounge at ORD which is awful. I was traveling last year in QR J along with a companion also in QR J who is OWS. It took some pleading but the agent at the ORD BA Lounge did let us in though she said if it got crowded we'd have to leave. Similar argument there with QR not paying for access. For a premium airline QR contracts with some terrible lounges in the US.

Try flying domestic AA and attempting to use the BA lounges at SEA or IAH, lol

Going off of this, I have heard that similarly, in SFO, Air Berlin contracts out the AF lounge, yet there are three other OW lounges there. The CX one being particularly empty 90% of the time as their flights don't leave until midnight, can they really deny access when the terms of OW state any business class passenger has access to OW lounges, seems ridiculous.

The operating carrier always pays, not the programme, in oneworld. The idea is that the operating carrier should be grateful that oneworld is supplying it with more customers because the customers want to use the lounge network.

J pax should gain access on the same level as OWS.

BA lounges in North America are very reluctant to admit non-BA pax. They'll say anything to get rid of you.

BA lounges everywhere are notorious for rejecting OW passengers
not traveling with them...

My understanding over the years has been that OneWorld lounge access policy is status-based. That is, any OneWorld Sapphire member can use any OneWorld airline business class lounge when departing on a OneWorld flight, regardless of class of service. Likewise, any OneWorld Emerald member can use any OneWorld airline first class lounge when departing on a OneWorld flight, regardless of class of service. Since you do not have OneWorld Sapphire status, you were not eligible to use a OneWorld lounge. Separately from status-based access, the operating carrier provides lounge access based on class of service. Since you were flying QR J, you are eligible for whichever lounge QR contracts with for business class passengers.

However, I note that the OneWorld lounge access policy does say that you should have access via class of service:

As you concluded yourself, the access is either status based or cabin based.

As a BA Gold (plus CX DM and QF Plat, although it shouldn't matter)...I was also just refused access to the BA Lounge at BOS while flying CX (in paid J). The reason is, "the lounge becomes a CX lounge only at 21:45". I said, I'm not trying to access the "CX lounge", I'm accessing the "British Airways Lounge" during its official opening hours ("Daily: 05:00 - 08:00, 10:00 - 13:00, 14:30 - 01:00").

It's literally...BA Gold refused access to BA Lounge while flying oneworld. nothing related to capacity - the lounge was at most less than 50% full when I looked...

Unbelievable.

My mom and dad are both ba gold, and flew sea lax hkg in j. Denied access in ba sea. They dont know rule. Just sit in food court

That's compensation-worthy, surely? BA Golds in a BA lounge?

Not necessarily. If they were ticketed on SEA-LAX on Alaska which isn't a OW airline I can see why the BA Lounge at SEA wouldn't let them in.