To slay something can mean to kill it or to amuse it. The past tense of the first meaning is slew, while the past tense of the second meaning is slayed.
The popularity of the word slayed has grown considerable in the last century, and my guess would be that the colloquially usage of the word will make it into the dictionaries eventually.
Also, keep in mind that slew has other meanings such as, a sudden change in direction. A slew of things is a large amount.
“She slayed them – hilarious, warm, a total pro and an extraordinary performer,” said Chris Silva, executive director of the Bardavon. “She will be missed.” [Poughkeepsie Journal]
A decade and a half after Wheatus slayed the charts with their catchy anthem, ‘Teenage Dirtbag’, One Direction have produced a rather tamer, but oddly catchy cover version of the fiery single that made Wheatus the darlings of the MTV generation. [Lancashire Telegraph]
Now, because we’re too stupid to know better, he credits himself as an anti-drug crusader, as if he slew that dragon, when he nurtured it. [New York Post]
Today our adventurer and traveler can tell the stories how he slew shark with a tripod camera. So the conclusion is: live in the city, buy houseboats! [Arch Daily]
The Waynesboro Police Department has arrested several members of the same family after they were involved in a slew of thefts in the city recently. [NBC 29]
Crash investigator PC Stephen Wootton said the car clipped a verge on the central reservation then slewed across the carriageway before hitting a tree on the nearside and flipping over to end up back on the road. [Hamspire Chronicle]