Having cleared this this one with the powers that be...
"The Dogs Bollocks"
I had no idea of the origins or root of this - simply that it is in common use (vulgar) an NOT for polite conversation!, for 'the absolute best'. Generally applied to an item, but can be extended to exciting experiences.
eg. "His car is T.D.B." or "That flight was T.D.B."
TDOL moderator added: (edited)
I think the origin is from dog owners noticing the amount of time the average dog dedicates a day to licking his testicles.(Bollocks)
1- This idiom doesn't carry the same meaning- it refers to a specific characteristic, the ability to remain calm under pressure, but it doesn't go further than that.
2 & 3- This aren't idioms, IMO, though they do have a similar meaning to A-1, but don't mean the best, just high quality.
4- This would be 'top-rung'. You wouldn't be top of the rung. 'Top-rung' is used to mean the best, but I haven't heard it used for people, but positions and for the qualities of things like systems, tasks, etc.