The paralegal does not appreciate the joke, and lets the lawyer know as much. In response, the lawyer simply moves the decorations adjacent to the paralegal's workstation. Around the same time, the lawyer also starts asking when the paralegal intends to retire.
Four(!) years later, the law firm's office manager fires the paralegal after years of documented performance issues. Citing the diapers-and-wheelchair incident, she sues for age discrimination, claiming that while the lawyer did not make the decision, she was the "cat's paw" by causing an unbiased decision maker to take the adverse action.
The 6th Circuit affirmed the dismissal of the lawsuit because there was no evidence that the lawyer "intended" to cause the paralegal's termination. To the contrary, the lawyer was on the record against prior discipline taken against her, and had written her a largely positive performance review. Thus, it would have been unreasonable for a jury to conclude that the lawyer intended for the office manager to fire the paralegal, diapers and wheelchair notwithstanding.
Jokes that use an employee's protected class as their punchline are best left as far away from work as possible. This case ultimately worked out in the employer's favor, but at what cost. Today's joke is tomorrow's deposition or trial exhibit if and when the employment relationship sours. Why take that risk? Further, legal risk aside, why risk offending an employee, whether that offense is or is not actionable?