Well, I did know what it meant - which is not exactly what Boris is using it to mean, so he is not quite as clever as he thinks he is.
I'm sure he didn't mean to inform us that Corbyn uses the withdrawal method of contraception when doing his duty to help a widowed sister-in-law to conceive a child who, under Old Testament tradition, would be considered to be his dead brother's child and thus inherit said brother's estate (rather than it reverting to him)
What is this obsession of his with masturbation, anyway? Spaffing up walls, Onan - did he spend any time actually learning anything at Eton?