Since I have experience being a goofball I thought I could do some commentary on the subject.
It is a fine line to tread, trying to keep an air of delightful charisma while tripping over ones own feet. Lose the charisma and you look like a compleat ass.
A well aimed cream pie here and there. Make sure your target is in on the joke or the tone in the room can drop to a hushed tension.
Sometimes the right expression seals the deal. Professional clowns know this technique well and have developed painted expressions that put their entertainee in the desired emotional mood.
Good clowns can be good fun. What is a good clown? Well, for certain, a good clown knows exactly what they are doing. Their seemingly clumsy behavior is indeed precisely calculated. It is an exact science, if you will, as it were.
All in all there is quite a bit to admire in such an individual. As a clown is indeed that, an individual that is. That is to say that there is little to suggest that clowns accidentally fall into their profession. It takes determination and great skill to become a successful clown in our day and age. For that, good clowns have my respect.
The bad ones? Well, I've never seen a bad clown really.