How can I avoid such an embarrassing situation like my sister's friend catching me jerking off in the future?

Always make sure you are in a private space. If you're at home, lock the door of your room. And be more aware of your surroundings. Don't engage in such private activities in common areas or places where people might unexpectedly walk in.

Always make sure you are in a completely private place. Check the locks, close the curtains, and listen for any signs of someone approaching. If you live with others, establish clear boundaries about personal space and privacy. Also, be aware of the time and the likelihood of others being around.

First, you should be more aware of your environment. Check if there are people around before you start any private activities. Second, respect the privacy of the place. For example, if it's a shared space, don't do private things there. And finally, if you feel the urge to do something private, find a secluded room like your own bedroom and make sure the door is locked.

Lock the door. It's the simplest and most effective way. Make sure your room is locked whenever you want some private time.

You could try to keep a bit more distance from her in the future. If you're all sitting together, make sure there's some space between you. Also, be more aware of her body language. If she seems a bit uncomfortable or like she might have some digestive issues, it might be a good idea to excuse yourself for a moment.

This is an extremely embarrassing situation. First, you should immediately stop what you're doing. Then, try to apologize sincerely for making her uncomfortable. Avoid making excuses. It might also be a good idea to keep your distance from her for a while to let the awkwardness subside.

Just be aware of social norms and common decency. Know what is appropriate to talk about and what is not.

This is a very embarrassing situation. First of all, you should immediately stop what you're doing. Then, you might need to sincerely apologize to her for making her uncomfortable. Try to keep your distance from her for a while to let the awkwardness subside.

Be conscious of the boundaries. Know what is appropriate to talk about in different social settings. For example, in a friendly gathering, focus on common interests like movies, books, or sports.

One way is to be conscious of the social environment and the people around you. If you're in a professional setting, talk about work - related things. In a more casual setting, like at a coffee shop, you can talk about travel experiences. Also, if a conversation starts to veer into inappropriate territory, gently change the subject to something more positive and acceptable like new music releases.