An established couple is having a lovers tiff and their coworker is annoying them? They go to this historical museum and see this gigantic wooden dildo. The annoying co-woker gets sucked back in time and meets this giant, it it turns out said co-woker is the one who created the giant wooden dildo (for aforementioned giant). Meanwhile, back in the present co-wokers ancestor (who looks just like him) helps the couple resolve their problems. Co-worker/ancestor switch back, and all is well in the world.

At first I thought it was by Sakurai Shushushu, but I can't seem to find it. Help!

You were right about the artist. I think its chapter 6 of Jungle King. I always remembered that because it was so random lol

I think you may be right. I'm DL'ing it as we speak! Thanks. 🙂