"RIP spotting" refers to spotting and reporting "rips" (submissions which plagarize existing pixel art/sprites, in part or in whole) to the moderation staff.

Take the well-known 8-bit Mega Man sprite as an example. If someone edited the sprite in some fashion and posted it as a PJ submission, it would be considered a "rip" and thus be subject to deletion.

All works posted to PJ must be the work of the artist alone. You can take inspiration from other works (pixel or otherwise), but you can't rip them off.