Lisa's all like BAAAAAAART! while Allison's all like Wow, so that's what it looks like teehee instead, but pretending to be more like zOMG, I did NOT just see that =^^= so that Lisa won't think she's perving on her bro.
Bart is so relaxed right now...I could just imagine things going horribly wrong if, say, Snowball II were to suddenly dive-bomb on him from the roof!
I don't think she actually has. I don't recall seeing her around whenever Bart does one of his 'mooning' stunts, and I dont think she was there when he did his skateboard-streaking on the movie either. Either way, she's missed a lot.
That was just a joke. In fact, believe it or not, she has. In the Simpsons Comic, Wall or Nothing, when the entire town goes skinny dipping, she's one of the skinny dippers. She's probably seen Bart and the other boys naked for the first time.
Depends on her thinking here. Shock at suddenly seeing a naked boy; extra shock at seeing someone she actually knows naked; and probably using the scientific, inquiring part her mind to think "So THAT'S what boys look like!"