She's already giggling when he starts looking around like a puppy who has lost their bed and then he is giving her quite the view and she can't help laughing outright again. An ass wound is objectively funny all the time, always. No one can blame her for laughing!

"There's a joke here about an asshole... oh wow, that's a really perfect spot to get stabbed. Was the tattoo before or after?"

The rest of her scars courtesy of Alex's family and her wedding night are also visible thanks to how skimpy her bikini is, but usually her hand is the shining star. Plus she's got all her fun and stupid tattoos to focus on usually.