With DP it motorbikes. His bike gets cleaned and polished and put under it's special cover - although he'd much prefer a garage, in fact, he'd bring it in the house if I'd let him!
He's forever fixing or tinkering with it, buying new bits for it (whilst complaining he had no money - and when he does have money it always goes on the bike before considering anything else he needs, like clothes for example!).
And he changes bikes constantly - in a year he has had 8 different bikes (at one point he had 3 at once - add in my one and my 'parts donor bike' and we had FIVE bikes on our tiny patio garden! 
)
And of course, each new bike needs new bits for it. As soon as it's all fixed up, it's like he gets bored and sells/swaps it for a new one and he cycle all starts again; testing, taxing, registering, new bits - all money money money.
If anyone else he knows needs help fixing their bike, he's there helping. Never gets paid for the hours and hours and hours of work he does on it; he does it because he adores it.
I loved his last bike (Kawasaki Z1000), and it was so comfy when I went on the back. He seemed to one it too, when all of a sudden he decided to swap it for another one. New one (Kawasaki ZX1200) is SO uncomfortable for a pillion as the foot pegs are so high and his riding position is lower meaning I'm sat up in the wind more. Although being pregnant means I can't really continue to go on it for much longer, which is sad because I love going out with him - totally different to riding myself - but at least I don't have to admit how much I hate this bike!
I have my own bike too, and love going out on it (although not so much now obv.), but his obsession is bonkers!
Still - I knew this when I met him and I do love that he's a biker rather than a gamer! 