Indeed. Given that OP is kindly treating us all to lessons in 'Contract law for vexatious litigants', this is an area I would also be interested to hear more about.

OP's 'friend' wasn't denied lounge access, but rather access to the lounge of his choice. Sounds like something even a US jury would evaluate as a loss of $0. So far as I know, Oneworld does not promise that lounges will have any particular characteristics, e.g. concerning what facilities/food/drink etc. will be available, and as we know many of them are somewhat basic to say the least. So how is access to the BA lounge worth more than access to the Virgin lounge?

Presumably OP thinks that if he turned up at the T5 Galleries North and was told it was shut for redecoration but he'd be welcome in the lounges at the other end of the terminal, he could sue BA for his disappointment in missing out on his preferred lounge.