The champion is definitely this:

    alias s='cd ..'

This was enabled by default in some distro, I think it was Mandrake Linux. I learned to use it and now I can't live without it. 's' is always ready to be immediately pressed, and it can even be spammed.

    export EDITOR=vim

    function highlight() {
        egrep --color "$1|\$"
    }

    function mkcd() {
        mkdir $1
        cd $1
    }

    function git-cite() {
        git log -1 $1 "--pretty=format:%H (\"%s\")%n" | sed -e 's/\([0-f]\{12\}\)[0-f]*/\1/'
    }

    alias gd='git diff'
    alias gpr='git pull --rebase'

(and a bunch of other similar aliases)

    function gcmr() {
        git checkout origin/merge-requests/$1
    }