Luffy
Luffy would react with a mixture of shock and delight when his significant other sat on his lap. The suddenness of the action may have surprised him at first, but once he realizes what's going on, he's probably going to smile broadly. Given his carefree and impulsive nature, Luffy would find the situation entertaining. He could jokingly put his arms around his significant other and give them a firm squeeze, expressing his love in his own special way. All in all, Luffy would greet the occasion with his usual warmth and determination.
Zoro
Zoro may look surprised at first when his significant other sits on his lap. He might wag his eyebrows or give them a suspicious look. Zoro, though, is not one to display a lot of emotion or affection externally, so he might keep his cool. He may also experience some initial discomfort or awkwardness because he cherishes his privacy. Knowing Zoro, though, he would quickly adapt to the circumstances and make an effort to ensure his S/O was comfortable.Zoro could put his arms loosely around his sweetheart's waist to give him stability and security. Even though he might not publicly express his feelings, his deeds would say a lot. He may recline a little to find a posture that suits him and his significant other. Even though he doesn't express it visibly, Zoro would value physical proximity and intimacy.
It's critical to remember that Zoro is a unique person who cherishes his privacy and independence. Therefore, it's wise to always get his permission and make sure he feels comfortable making this kind of physical contact.
Sanji
Sanji would react very differently from Zoro when his significant other sat on his lap. Given Sanji's passion and romantic nature, his reaction would probably be a mixture of surprise, delight, and subtle flirtation.
Sanji would most likely be surprised at first, his eyes going wide with shock before a beguiling smile appeared on his face. He would quickly encircle his significant other in his arms and draw them nearer to him.Sanji would be ecstatic about the chance to be physically near his significant other and would probably show it by giving him tender pecks or cheek kisses.
Sanji might also indulge in his flirtatious side, using this as a chance to show off his charm and chivalry. To make his significant other feel special and loved, he could whisper kind remarks in their ear or playfully tease them.Sanji would savor the private moment spent with his significant other because he values beauty and romance in life. It's crucial to remember that comfort and consent are crucial in every circumstance, so it's advisable to talk and make sure that both partners are comfortable with this level of physical contact.