As the above examples testify, the great majority of sexual double entendre songs involve various different trades and over the centuries scarcely a trade has escaped this treatment, the tools of the trade usually being instrumental as it were.

However 50% is rather an exaggeration. Certainly more than 50% of songs involve amatory encounters of some sort, but probably less than 25% actually involve metaphors of this type. A few of the above examples are not really sexual metaphor, or at least in their earliest versions. In the earliest version of The Foggy Dew, for example, it's a 'bugaboo' or a ghost which is light heartedly frightening the girl to get into bed with him, not really a metaphor as such.

Those people who read sexual metaphor into nearly everything ought to get out more.