Let's say Ted owns a website.

Can his friend, Harry, display his Adsense ads on Ted's site? (with permission obviously)

This isn't against any terms and conditions, right ?

His adsense ads? What do you mean? You mean his own personal ads ones via Google Adwords? I don't think you can choice preference over who displays on your site, just who can't display.

If your friends wants to put his own ads on the site then it's fine, just as long as their easily distinguishable from Googles ads.

It's not against the rules. Even if it were, it's not like they could know if you are or aren't operating the website the ads are appearing on.

that's ok and not against google rules. but if he click it .... that's mean suicide.