Electricity requires a potential DIFFERENCE to flow. If your entire body is at the same potential, no current flows anywhere.
Potential is also a quantity that only has meaning in terms of a difference. You're free to select the "zero" of potential anywhere you'd like.
If you touch the + terminal of a 1000V battery, you're at potential of 1000V with respect to the - terminal. Of course, you're also at a potential of 0V with respect to the + terminal. Both descriptions are perfectly valid and correct.
All that being said, I'd advise you not to go grabbing the hot wire in your house's electrical system -- 120V can jump across sizeable air gaps, and you'd have a really hard time truly isolating yourself from ground.
Will i get shock if i'm wearing tenis shoes and touch the + at the same time? Since shoes are good insulator, i shouldn't get shock right? Does cerment conduct electricity? I'm guessing all things conduct if the potential is high enough.
So how come birds doesn't get shock when pirch on power lines? Is it possible for them to get shock even though they are not touching the ground or other wires?
Birds don’t get shocked when they perch on power lines because they do not provide a good path for the electricity to get to the ground. As said above electricity requires a potential difference to flow. A physical analogy is close to this. Lets say you wanted to drop a ball from some height to the floor. You let the ball fall. I will fall until it hits the ground. Applying this to electricity. Have you ever seen a squirrel running across a power line after a storm? Personally I haven't but I can guess. The wet squirrel unlike the bird can provide an excellent path for the electricity when crossing from the power lines (high potential with respect to ground) so some other object, tree or pole (ground). Anyway there would not be much let of the squirrel. Lesson to be learned, ahhh "better squirrel trap"?