A "ludicrous idea" means a thought or suggestion that is really silly, absurd, or unbelievable. It is so ridiculous that it is hard to take seriously. Full definition
Now that our collective nerd hearts have calmed — for the most part — and we can attempt to go about our normal lives while subsequently imagining a giant flaming iconic logo, we as gamers and fanboys find ourselves in one of the most glorious moments in gaming history once again; that indefinite haze of pitching ludicrous ideas of who needs to be on the latest Super Smash Bros roster! (cogconnected.com)
Glad to see that for a guy / gal who routinely dismisses me as a lightweight with ludicrous ideas and statements, you pay so much attention to my words... almost as soon as I submit them... otherwise you would ignore me and this conversation would not be ongoing. (remonline.com)
Unfortunately, most of those who call themselves skeptics, espcially those who blather on and on about the end of global warming while swallowing the most ludicrous ideas hook line and sinker, would be better described as fake skeptics. (tamino.wordpress.com)