The sentence is humorous or ironic on several levels, primarily due to it playing with the concept of self-identity and absurdity in contemporary socio-political context. Caitlyn Jenner, a transgender woman, was known as Bruce Jenner before she underwent her transition. In the joke, Caitlyn is accusing her pre-transition self, Bruce, of touching her 30 years ago. This sentence is funny because it applies contemporary social issue language to an old situation.
Part of the humor stems from the fact that this sentence references a serious, sensitive and highly contested social issue: sexual harassment or assault claims, more specifically, ones from past decades. The sentence is ironic and potentially funny for some because it takes this serious and controversial issue and applies it to a seemingly impossible situation: a person accusing herself from the past life. It's ironic because pointing out the absurdity of accusing your own past self of wrongdoing challenges our understanding of social issues and the dynamic nature of personal identity.
It's also funny due to the cognitive dissonance it creates. It forces the reader to reconcile with two opposing ideas, which are Bruce Jenner and Caitlyn Jenner as different entities, despite them being the same person before and after transition. This element of cognitive dissonance amuses the reader as they attempt to make sense of a situation that goes against their conventional understanding of reality.
Furthermore, there's a level of irony where the pre-transition identity (Bruce) is being accused by the post-transition identity (Caitlyn). Usually, when accusations are made, there's a clear differentiation between culprit and victim. However, this sentence blurs that differentiation in a humorously confusing way, and it questions some fundamental beliefs about personal identity, accountability, and blame.
The sentence also presents a humorous commentary on the prevalent trend of outing people involved in controversial acts several decades ago. While the resurfacing of such events often serves to hold perpetrators accountable, this sentence leverages the trend to create humor in a more absurd context. It seems to mock the idea of hindsight bias and the unreliability of perceptions over time.
Lastly, the timing is crucial to the humor. It stipulates "30 years ago", which is a time when Caitlyn Jenner was living as Bruce Jenner. This adds a layer of ironic impossibility, thereby making this sentence funny. The humor lies in the implicit absurdity of Caitlyn making such a claim about a time when she was, physically and socially, still Bruce Jenner. It encapsulates the incongruity theory, where humor is derived from bringing incompatible scenarios together, creating a ludicrous twist. Things Are So Messed Up Now Caitlyn Jenner Is Now Saying Bruce Jenner Touched Her 30 Years Ago