111: "I'm up for that" "I'm down for that" Mar 29, 2015

Slang words and phrases follow no strict rules, neither in grammar nor logic. As such, the two common phrases, "I'm up for that", and "I'm down for that" can exist and mean the exact same thing of, "I am willing, even eager, for any given thing". Regardless of the level to which English is nonsensical and convoluted, it, in this case, is not entirely to blame for such recently created slang words and phrases.