When does caffeine make you high? It just makes me jittery and easily agitated, so when I make a mistake I feel like throwing the computer out the window.

Aside from developing a physical addiction, I respond well to caffeine. More of it generally makes me happy and stimulated.

More or less drinks for functional/mostly-functional languages?

More for anything obnoxious like PHP or IE Javascript incompatibilities. Fewer for things that are hard, but not evil (including functional languages).