wait
Explanation
The Joke
The comic sets up what appears to be a classic "caught cheating" scenario. A man walks in on a woman with another man, and the woman immediately blurts out the cliched line "Wait! It's not what it looks like!" But her speech is slurred -- she says "Ith not wa it lookth like!" and then notices "I canth feel ma tongue!" The caption below reveals the actual situation: "It was the worst possible way to find out my brother had stolen my numbing condoms."
The twist recontextualizes the entire scene. The woman is not making excuses for infidelity -- she genuinely is telling the truth that it is not what it looks like. Her slurred speech is caused by numbing condoms (which contain a mild anesthetic, typically benzocaine, meant to reduce sensitivity). The brother stole the narrator's numbing condoms and used them, and the numbing agent has transferred to the woman's mouth, implying oral contact.
The Humor
The joke operates on multiple levels of misdirection. It starts with the most tired sitcom trope imaginable -- walking in on a partner with someone else -- then subverts it by making the slurred speech not a sign of panic but a literal physical symptom. The phrase "worst possible way to find out" adds another comedic layer: the narrator's primary concern is not the scene itself but the discovery that his brother has been pilfering his specialty condoms. The comic also plays on the absurdity of numbing condoms as a product category, taking their real-world existence to a ridiculous logical conclusion.