I think the love shake is characterized by the smaller male turning perpendicular to his mate (like on his side, with his head facing the female) and shaking violently. When I first saw it, I thought my fish had epilepsy.
I have never heard of a clown doing that when it is alone though.
Also, my understanding is that a sole clownfish will turn into a female and if you want to add a fish down the road, then you must get a very small juvenile male (preferable one that has been kept with many other juvenilles) so there is no chance it is female.