Usually, sexable girls aren't even willing to do it. Guys just assume they are, so they try,and usually fail.
Girls who are looking for relationships oppose to just messing around are known as "Not sexable".
Josh: Mhm.... *thinking: wow she's totally "sexable"*
George: why won't you do it with me?!! we've been going out for 2 whole days!!
Rachel: George, I met you last week! I am NOT sexable!!