Tits.
And f***.
See this:
http://www.nailmaster.ru/f***.html
(WARNING: The above link contains swear words, that may be offensive to some viewers).
Claratis. Likewise, a favourite concept.
As for least-favourite, I will go with the curt monosyllable of my own name. Conjure is pretty bad too, as are most words with the letter J.
Tits.
And f***.
See this:
http://www.nailmaster.ru/f***.html
(WARNING: The above link contains swear words, that may be offensive to some viewers).