give somebody a hammering: beating somebody or punish someone severely.

in stitches: laughing really a lot.

sick as a parrot: extremely disappointed

Note: correct me if I'm wrong : sick means ill (especially in american english) 

                                           sick means also "vomit" (especially in british english)

eg: in hospital: Patient: Nurse, nurse! I am going to be sick!

                     Nurse: That's why you are in hospital, Sir!    LOL

"Tell porkies" is derived from Cockney rhyming slang. Pork pie = lie; "He's telling pork pies again...." Over time this became abbreviated to "telling porkies."

Other examples:

"Have a butchers" = "Have a look". The original rhyme was "butcher's hook = look". Over time we've dropped the 'hook' part and now just say simply 'butchers': 

"Climb up on the wall and have a butchers at what's happening on the other side...."

"Barnet" = hair. The original rhyme was "Barnet fair = hair". Over time we've dropped the 'fair' and now just say simply 'barnet':
"I don't think much of your barnet...who cut it, Stevie Wonder?"

Loaf = head (Loaf of bread = head): "Use your loaf and figure it out...."

"Syrup" = wig (Syrup of fig = wig): "Have you seen his syrup? What a sight...."

Rabbit = talk (Rabbit and pork = talk) = "She kept rabbiting on for hours and I couldn't get away..."

"China" - mate (China plate = mate)... 'Hello my old china, how are you? I haven't seen you for ages..."

You're welcome Teja

Not bad at all, but I think the following sounds a tad better: "Thanks Ben. I am learning a lot from this discussion. I look forward for some more..." 

a few more: 

Jolly good: very good

Smell a rat: suspect that something is wrong or someone is dishonest and is trying to deceive you.

giving somebody gyp: causing pain. <em> I had a fall and my leg is still giving me gyp</em>.

make a pig's ear of something: execute something really badly.  <em>the carpenter made a real pig's ear of that tableT</em>

Thanks Ben, got to learn a lot from your disscussion.looking forward for some more...

correct me if i am wrong anywhere.

Valentina.. Prego ;)