A "bright spark" is either genuinely clever or, more often, a sarcastic jab at the absolute genius who’s just done something daft. Tone is everything: said warmly it’s praise, said with an eye-roll it’s blame. Proper British classic for calling out bad ideas without saying you’re raging. Honestly, it’s polite shade at its finest.
"Which bright spark put the BBQ in the conservatory? Now the smoke alarm’s having a meltdown and Gaz is fanning it with a copy of The Sun"