Finn just has that build, a bit beefy but with round edges, so his chest must be amazing, and the first time Poe sees it he just wants to go to town

And when they get together, he does. He bites his pecs, licks his nipples and sucks on them, squeezes the soft-hard muscle, even convinces Finn to let him fuck them

and Poe gets so desperate and horny when he sees Finn's fabulous chest that Finn can't say no

+bonus if Finn's nipples and chest are super sensitive and he's just as turned on as Poe is when Poe plays with them