My AP biology teacher always told her students how she thought "plasmodesmata" was the sexiest sounding word in the English language. Of course, if you are into biology and know what plasmodesmata actually are, then you know her opinion was based on the sound of the word alone.
Pulitzer prize winning poet and novelist, Sylvia Plath, maintained that the most euphonic word in the English language is "syphilis." Plath, too, was obviously basing her opinion on sound alone. Repeat it outloud a few times and you will see where she was coming from (if you can ignore the connotation and if your significant other isn't within earshot). I don't think syphilis counts, however, because "euphonic" and "sexy" may or may not be synonyms depending on personal taste.
I submit that the sexiest words in the English language are officially, "You take it easy tonight, Hon. I'll put the kids to bed." I have a big smile on my face right now just thinking about them.