By Nick Bryant BBC Washington correspondent travelling with President Bush

I well remember the first time I ever saw the German Chancellor Gerhard Schroeder shake hands with George W Bush, for it had all the awkwardness of a pimply teenager trying to steal a kiss from his date on the back row of the local cinema.

The hawk-faced chancellor was stood on the pavement outside an awfully trendy Berlin coffee shop, when the president's armoured limousine pulled up to the curb-side.

Mr Bush leapt out, shot his trademark grin - part smile, part smirk, head bobbing slowly up and down - and then gripped the chancellor's hand.

Mr Schroeder clearly had no idea what to do.

Presidential protocol

At first, he reached behind the president's neck, seizing it in a vice-like grip.

But perhaps deciding that a presidential neck rub might breach diplomatic protocol, he grabbed his upper arm instead.

Germany's anti-war stance and a Hitler row have hurt once-warm relations

But then Mr Schroeder decided to get all familiar again, lunging forward to embrace the president in a mighty, Germanic bear hug.

Then, just as he was about to bury his head on Mr Bush's shoulder, the chancellor froze pre-clinch.

To hug or not to hug.

It was clearly a question which had not only paralysed his mind, but his limbs as well. It was painful to watch. A cringe moment of the highest order.

The German chancellor arrived in Prague for Nato's summit not quite knowing this time whether he would even get to the touch the president, let alone hug him.

His opposition to a possible war on Iraq - voiced most loudly in the run-up to the German election - infuriated the White House.

And the president was said to be hopping, Texan mad by a remark attributed to the chancellor's then justice minister comparing his political tactics to those of Adolf Hitler.

When Mr Schroeder eventually won, Mr Bush pointedly refused to place a congratulatory phone call.

Donald Rumsfeld, the US Defence Secretary and Bush administration geopolitical hit-man, said that relations between the two countries had been poisoned.

Diplomatic outcast

So when we were handed the president's schedule for his three days in Prague, it came as no surprise that the errant chancellor's name was missing from the list of leaders whom Bush planned to meet one-to-one.

Mr Schroeder apologised for the Hitler row but was Mr Bush listening?

It amounted to the diplomatic equivalent of school detention or 'lines'. Write a hundred times - I must not annoy the president. I must not annoy the president.

On the eve of the summit, when Nato leaders posed for the "family photo" during a black-tie dinner in the opulent setting of Prague Castle, Mr Schroeder found himself positioned just about as far from the president as possible - a diplomatic outcast, on the fringes of the group. They did, we are told afterwards, shake hands.

Ari Fleischer, the White House spokesman who arrived in Prague fresh from his honeymoon, said: "It was a very nice social encounter".

'Cordial' and 'Professional'

But cordial was clearly the word of the day.

Mr Bush took the initiative at a photo opportunity in Prague

The president said the meeting had been "cordial" and added: "We greeted each other cordially."

Inadvertently, Mr Bush may well have introduced a new verb to the diplomatic lexicon.

To Cordial: to pretend to be civil to someone you clearly despise. Use: last night, the chancellor received a cordialling from the US president.

The Germans are describing their relationship with America as "professional". Yet while Mr Bush occupies the White House, it is unlikely ever to become warm.

Beware a president bearing grudges

This is a president who bears grudges, and seemingly has an elephantine memory.

Family honour: Ann Richards taunted Bush Sr and was ousted by Bush Jr

Ask Ann Richards, the brassy and sassy former Governor of Texas, who in 1992 described the first President Bush as a politician who was "born with a silver foot in his mouth".

Two years later, after a bruising battle for the governor's mansion, George Bush Jr turfed her out of office.

Ask Saddam Hussein, who ordered the assassination of his dad.

So clearly an example is being made of Mr Schroeder.

His very public and very humiliating scolding is intended by the Americans to send an unambiguous message to other countries planning to defy Washington.

It is meant as a reminder that the Bush Doctrine - you are either with us or against us - applies to allies as well as sworn enemies.

One of the great luxuries of being the world's superpower is that you can issue such stark warnings.

One of the great problems for Germany is that Mr Bush means what he says.