I really feel for you. I've dealt with people like that myself; despise them. Those noisy, disrespectful potties too high to realise they're affecting people around them. In the UK, there's a number you ring for noise disturbances. You might be able to chase that up and get in a device that registers the decibles. If it's deemed to high even for during the day, something legal might actually be done about it.

I hope they piss off and leave you in piece. Really annoys me that people like that exist, when here I am, even during the day, making the effort to be quiet for the woman below me. I generally do my best to be quiet and courteous to those I'm living with, but unfortunately, not everyone is so inclined. I play games myself, but there are these magical things called headphones, 'though I suppose that doesn't help much if it's a multiplayer game that other people are locally partaking in.

If it's a next door thing, try putting up "artsy" rugs... I read in an article that students do that and it actually helps to block out some of the noise. Unfortunately, it probably won't do much for the bass.