Predominantly used in London.
To 'clock' is: to realise, to catch on, to notice.

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed

Beaten, bashed, punished. To hit someone.

Observed, recorded, noted. Possibly related to determining the speed of a car by using a stopwatch to time its travel between two fixed points, such as "He was clocked doing 60 in a 45 zone".

To get caught out, usually by feds (police)

To completly smash a video game. Meaning you get perfect scores and without losing a single life.

Coming from the definition of being punched in the face and knocked out, clocked is a new stoner metaphor for when one is cooked and tired.