Lisa does get mocked for her huge backside but she kinda just rolls with it, it doesn't bother her very much unless someone's being rude or insulting. Lisa has the strongest self esteem and body image of the girls so she's really unfazed by it or maybe even will playfully retort back, she's aware of how big it is and so to her she finds people making fun of her behind or hips or thighs as kinda silly cause their just stating the obvious. "Sure yeah, me behind is proper huge! But I'm grand with that, you're the one making an arse of yourself standing there gawping."

Lisa was never bullied for it like Vicki was, Lisa was actually popular, so Vicki is way more defensive about people teasing or insulting her body then Lisa is.