Your kidlet is doing exactly what he's programmed to do for the next few years – explore, investigate, discover and learn. It's not bad behavior, it's normal, but some children are much more persistent than others.
But not all exploration is safe or practical, so parents must stay alert. I don't believe in spanking as a general discipline tactic, but I did give my daughter two "panic" swats when she was little, once when trying for the xth time to go into the street, and once when she became overly interested in an electrical outlet. I felt bad about it, though, and generally used the "remove and redirect" technique. As my daughter's comprehension grew, she learned that certain things were off-limits, and accepted those limits.
I always avoided saying NO! to toddlers, because it becomes a power word that they will use far too much starting around the age of two. What I did, as immediately and consistently as possible, was to gently and firmly grasp their hands, removing them from the object of interest, wrapping them across their chest, and pick the child up and set him/her down in front of some allowable item of interest. (You can also lead a child away if he will come willingly.)
It is often necessary to do this several times in a row, but the child, in my experience, has always given up. Only once with a tantrum in my case, but some kids could be more easily frustrated and enraged, so if a tantrum ensues, just ignore it calmly.
I've become acquainted with a few 'frequently popped' children, and find two common outcomes – a disengaged, quiet child who does not interact much with the world around her, or a driven, intense and challenging child likely to scream and/or "pop" the people who thwart her. I can't be sure, but it seems those are unintended consequences of relying too much on physical discipline.
This may not work for you, but I know quite a few young parents who do NOT expect to go to other people's homes while their toddlers are still in that unrestrained exploration stage. You might consider doing this – it will probably only be a few months before your son can start understanding distinctions between okay and not-okay things to touch. Or, when you do visit, just expect to have to shadow your child and grab him over and over.
One last thing that I always find effective: interact with the child with non-dangerous or not-too-fragile items, thus allowing him to satisfy his curiosity, so he can move on. Show him HOW to correctly use the object. I did this with my grandson, who wanted to "use" every cell phone he saw at around a year of age. Instead of having him beg and reach, I actually sat with him a few times and showed him which buttons would get what responses. He loved it, and after punching only a few other buttons with the apparent result of "Uh, oh, nothing happened," he learned to use the device "properly" according to Granny.
By the way, the earlier comment "all the development books are going to tell you is that this is normal (which we already know) THEREFORE you should allow it and leave all discipline until after two," is just not the case. All the books I've read (quite a few) recommend consistent and quick responses to undesirable behaviors. But most of them don't recommend popping or spanking, but rather removal and redirection. That's discipline, too, and it's effective.