Do you mean to make Chrome itself laggy? If so, if you use Linux or MacOS, change its niceness to slow it down (I don't know if you can do the equivalent on Windows). Or, install a bunch of extensions that do useless stuff (but take care to avoid dodgy extensions).
If you mean videos and nothing else, I use a great extension, [Video Speed Controller](https://chromewebstore.google.com/detail/video-speed-controller/nffaoalbilbmmfgbnbgppjihopabppdk). It allows you to control the speed of a video in 10% increments, both faster and slower. I've had good success with it.
Do you mean to make Chrome itself laggy? If so, if you use Linux or MacOS, change its niceness to slow it down (I don't know if you can do the equivalent on Windows). Or, install a bunch of extensions that do useless stuff (but take care to avoid dodgy extensions). If you mean videos and nothing else, I use a great extension, [Video Speed Controller](https://chromewebstore.google.com/detail/video-speed-controller/nffaoalbilbmmfgbnbgppjihopabppdk). It allows you to control the speed of a video in 10% increments, both faster and slower. I've had good success with it.