I'm searching for the correct term for the part of the selfish gene evolution regarding sexes. In nature, this means the evolution of the traits such as the ducks' adaptation to "trap" the drakes' penises in order to restrict the male from attending to other females.
Sexual Conflict is the word you are looking for!
Sexual Conflict occurs whenever the optimal mating strategy for the female and the male differ. For example, in Drosophila, it is beneficial for a male to mate as much as possible, while it is beneficial for a female to mate only a few times.
I would like to expand a little on Remi.b's answer and point out that there are two key forms of sexual conflict.
Sexual conflict arises when the sexes have different routes by which they maximise fitness.
In the case of the ducks (and many other species) the males increase fitness by mating as much as possible, whereas females may optimise fitness by slowing the males rate. These sorts of conflict where behaviour or phenotype of one sex is beneficial to one sex and harmful to the other is called interlocus sexual conflict: the effects of one locus have consequences for other loci. The bed bug is a fantastic example of coevolutionary dynamics between the sexes resulting from interlocus sexual conflict - males use traumatic insemination and females appear to have made multiple adaptations in response.
Alternatively there is intralocus sexual conflict; when the evolutionary interests of either sex differ within loci. In this case selection favours different alleles in either sex. Genetic covariance needs to be reduced for the sexes to be able to move towards their own phenotypic optima, with such sexually antagonistic selection leading to sexual dimorphism when covariance is reduced.