What if you're up in a tree with binoculars trying to hide your presence (similar to using stealth techniques)? Is that legal?
Yes, if it's your tree or if you have permission to be in it. Again, suspicious, but not a crime.
Now, what if a half naked coed walks by the window 20 times a day? Still legal?
It may be. You wouldn't stand naked by a window facing someone else's house and not expect to be seen. That's what curtains are for. Although there might be state anti-stalking laws that complicate a case like this.
The use of basic network security tools such as portscanners should not automatically be considered a crime any more than climbing a tree or using binoculars should be.