Okay ATOT here's an awesome riddle for you that I bet you will not get...

[EagleKeeper]

Just because he ordered the beer a moment ago, does not mean that is was drawn at that moment.

the beer could have also been drawn for some-one else and the man chose the wrong glass/mug.

Coming in out of the sun and removing the shades could easily affect his vision for a short time, especially if the bar is not inside.

/non drinker logic

 

[Law]

if you are not going to give us the answer, at least give us another hint since obviously no one knows the answer based on the hints you already provided us.

 

[TGS]

The eyes of the man in the striped suit is adjusting to the light difference from outside. He turns to talk to the man with sunglasses and knocks over his beer.

Or perhaps the man with the glasses is still wearing his shades, and knocks his own beer over turning to talk to the man in the striped suit.

Someone will have to give information if a spilled beer actually tastes flat on the ground.