Re: Tickling wierd?
Him getting hard may not be normal in the grand scheme of things.
In terms of your relationship I think the tickling has always been there. The physical reaction he has now while doing it, IMO, is just that. A reaction.
Tell him politely and firmly that you do not want this to continue.
~ The journey of a thousand miles begins with a single step ~
* Nothing in the world has ever been accomplished without passion *