1.) a dense puffy type of cloud, usually consisting of concentrated DUMB having a dull face and retarded outlines often piled up like an imbecile.
2.) a person who actively seeks to rain bullshit upon persons lacking a dumbrella.
3. Something so unquantifiably awesome that it can only be appreciated by the momentary retardation that witnessing it results in.
1 & 3) "Wow. That gaggle of oompaloompas just tried to sell me hamster insurance. How ridickulumulus is that??"
2) "No, considering you've tried to pull that one on me multiple times this week, I would say that YOU are ridickulumulus, dude."