Basically, the same as eyeballin. To look at something with extreme interest.

Also, the act of eyeballing something is to measure or weigh something without any tools.
(Not necessarily refering to anything illegal or obscene)

e.g.: «Dude! You see those chicks eyeballing your ride?»

e.g.: «Lemmie see. I'm eyeballing it. Looks like 4 1/2 feet from sofa to wall....where's my tape measure? Yep, it'll fit!»