Sharon Osbourne Now here's a lesson we're glad to be learning from a distance.

Never, ever say anything mean about Kelly Osbourne.

And no, it's not the tirade of bad expletives from dad Ozzy you should be afraid of.

Tis her mamma, Sharon, and understandably so.

According to The Sun, Shazza's let rip at comedian Jim Jeffries after he made some disparaging remarks about Kel.

Apparently Sharon's sent him an email telling him to "f*** off" for calling Kel "unattractive and fat".

The spat started when Jim made a joke to Kelly during this year's NME Awards USA, which he presented.

He joked to Kel that she wasn't as attractive as Agyness Deyn, who'd just walked off the stage.

Kel's said to have responded with some expletives of her own and then he says she spat in his face.

The Sun claims Jim has said: "I thought that would be the end of it but I got an email from Sharon which said, 'Dear Nobody. Wait until you're a celebrity before you criticise REAL celebrities. Why don't you f*** off .'"

Jim's reply?

He's said: "Dear Sharon. After you had all that plastic surgery and had the fat sucked out of your thighs, why did you pump it into your daughter's face?"

This has all been revealed in a gig Jim's been doing at Shepherd's Bush, where he talked about the email ranting on stage.

Sky Showbiz contacted Shazza's people who said there's no comment on the above.