[shawabawa3]

Not sure if it's only the UK but we also use "up" and "down" as synonyms in some sitations. e.g. "I'm up for going to the pub" and "I'm down for going to the pub" mean the same thing

[FroshKiller]

This is also true in the US, although I would add that being down for something connotes a tiny bit more enthusiasm than being up for it, since "down" is also used in the context of making a commitment, e.g. "put me down for two boxes" or "I'll mark you down as present."

[evgen]

The latter case is related more to 'writing something down [on paper]' than to a standard up/down usage that implies directionality.

[drewzero1]

And certainly being marked down has different connotations from being written up!

[lupire]

Don't forget markdown and markup!