One of the trends I've noticed in the millennial generation (based on the 'Transitions' project though this is not taken from that) is the shift of male sexuality away from being quite so polarised between gay and straight, towards a more ambiguous, less rigid interpretation. It's not that more men are likely to self-identify as bi-sexual (though that might be the case, I don’t know), more a trend towards not feeling the need to be quite so demonstrably 'straight'.
The insecurity associated with ambiguity is disappearing. In its place is a more nuanced expression that allows for the boundaries to be a little blurred. Women have long been OK with this flirtation; it's always been something that was permissible, perhaps even encouraged. It was incredibly risky for men to do this.
The two guys in this image self-identify as straight, yet in the context of a long night out in Brighton (which is known as the gay capital of the UK), after a lot of fun, in the early hours of the morning and in response to a random photographer goading them a little, the new masculinity is able to express itself like this.
I think it's something to be applauded (the expression, not the photograph, which is sadly compromised).