The second thing? That he's remarkably like the characters he plays. Whether it's discussing his bad habits, what it's like working with Cameron Diaz or getting older, he's as enthusiastic as a puppy and extremely honest. Possibly too honest.
"I pee outside," he announces, in response to the bad habit question. "I usually start my day by taking my dogs out and while they go, I go," he laughs. "I just feel like I'm connecting with nature. Man, tent, cave, pee, bush." He pauses and looks around. "Nobody else? Just me?"
As well as discussing alfresco bladder relieving, Ashton is in town to promote his new film, What Happens In Vegas. The film is a cheerfully dumb romantic comedy where a drunken Vegas spur-of-the-moment wedding turns into a full-on battle of the sexes when the couple win a $3m jackpot.
While laughing off the relative value of the jackpot - "in the UK, people are like, 'I can't even pay my rent with that!'" - Ashton can certainly see the mileage in the difference between the genders. And there's one subject that leaves him completely baffled.
"I don't understand shopping. It doesn't make any sense. As a guy, we decide that we want something, and then we go out and buy it. Women go to the store having no idea what they're gonna buy, or what they're even doing. It's not like you go, "I need a shoe", and you know what kind of shoe you need. You're just going to look at the shoes!"
Ashton and Cameron Diaz
Unsurprisingly, it wasn't the chance to analyse shopping habits that persuaded Ashton to sign up for the role. "I read the script and the first 30, 40 pages of the script, I was laughing out loud, really hard, multiple times. And when that happens, you have to stop and go, 'Okay, something's working here!'"
Getting him to sign on the dotted line though took a little producer jiggery-pokery.
"I was talking to Emma, one of the execs at Fox," reveals Kutcher, "and she said, "What's it gonna take for you to do this movie?" and I said, "Gimme a great director and a great co-star."
"She called me back a day later and said, 'Cameron Diaz is doing the movie!' And apparently Emma had called Cameron too and said 'Ashton's doing the movie'!"
It wasn't the first time the two stars had met but it was - and happily so for the audience's sake - a slightly more intelligible affair this time around.
"I saw her backstage at one of those award shows probably seven years ago. I thought 'Whoa, she's hot! And funny too! This is a hot funny person!'"
He laughs. "I don't think I was able to make words when I talked to her. I think I, like, just made noises."
If you were that keen to work together, how come it's taken so long to make it happen?
"She wouldn't work with me!" he grins. "I don't know if she will again...!"
