Why does "I'm down for X" mean the same thing as "I'm up for X"?
Same reason "fat chance" and "slim chance" mean the same thing
All languages are nonsense like that. From the five languages I ever learned English is the easiest once you recognize the general pattern of pronunciation (and Irish is the most overcomplicated whatever is this grammar who thought it a good idea)
National Funk Congress Deadlocked On Get Up/Get Down Issue:
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!