Paul Rudd talks boobs and gives dating advice in Rookie's Ask a Grown Man segment. (PHOTO: Screen Capture / Vimeo / Rookie)

Why are men so obsessed with boobs?

Leave it to Paul Rudd -- actor, comedian, screenwriter -- to answer that.

It's a good question, and I'm sure there's some kind of biological explanation, such as sustenance and when we were babies . . . breast milk kept us alive. There's also the thing of, we don't have them. So they're just interesting, Rudd says in a video, made for the online teen publication Rookie.

Maybe it's a combination of those two [reasons]. And then a third, maybe, just because they're awesome, he adds.

Rudd, 42, is the latest celebrity to be featured in Rookie's monthly segment, called Ask a Grown Man. Previous guests have included comedian Hanibal Buress and OK Go front man Damian Kulash.

Launched in fall 2011, Rookie is the product of 15-year-old fashion blogger Tavi Gevinson, who has made quite the splash in the fashion world with her personal site, The Style Rookie.

In the Q&A segment, which runs for more than four minutes, Rudd gives dating advice and shares his two cents on matching underwear.

Rudd is currently enjoying a multi-episode guest star run on Parks and Recreation, playing Leslie Knope's (Amy Poehler) city council opponent Bobby Newport. Rudd's next feature film is Wanderlust, a comedy also starring Jennifer Aniston, Justin Theroux and Malin Akerman.

Here are some highlights from Rudd's Ask a Grown Man segment. Scroll down for the video:

On when boys turn into men This is a loaded question. And I don't think an easily answered one. I don't think there actually is an age. I think that you'd find that there are many men who you would consider men, who actually are still boys. There's no line of demarcation. And every person is different. We don't have any kind of ritual that turns a boy into a man, like they do in some other cultures. And bar mitzvahs don't count.

On whether girls and guys can really be just friends I do. I really do. Seems like though, that kind of happens later in life. But I had friends when I was in grade school and junior high and they were girls. Yeah, I think you can.

On how to steal a man who is already attached Well this is tough, it's always tough. But I don't think you should do anything rash . . . Just be nice. Be his friend . . . Don't mess with something so that it could come back to you.

On matching underwear being a necessity I always wear it. Not always. I sometimes wear it.