whats a video of someone jerking off/reacting to a video called

A video that features someone performing an explicit act such as masturbation or reacting to explicit content is often referred to as an "X-rated video" or "adult video." However, if you're referring to a more humorous or meme-driven context, it might be called a "reaction video" or a "reaction meme," but it would typically feature adult themes. Please be mindful that such content might not be suitable for all audiences and is often restricted on many platforms.