'Roaringly upper class'?! 
Well, only in the UK where people are preternaturally obsessed with such things. In other countries, it's ... a name.
Cosmo Kramer for me, too. And the whole deal was, of course, that he kept his name hidden and went by Kramer because he - seemingly unembarrasable, if you know the character at all - was so embarrassed by it.
It's not a name I would ever use, but -- it's not that bad.