The MOST lewd game? I've played so many lewd games I don't even know if I can answer this. But if you want eroge recommendations I can recommend "kamidori alchemy meister" (It has actual gameplay and is fun!). Grisaia series is also pretty good storywise.
I guess Monster Girl Quest can be labeled as very lewd even in eroge category. It is a really good game anyways.
Artificial Academy 2 is also pretty nice game if you just want lewd stuff.
What is the most disgusting/shocking game you've played?