goodbye, farewell (with the wish of never meeting that person again)

hell-for-leather, at full speed, flat out, at full tilt

the more the merrier

law of the jungle, survival of the fittest, might makes right

(euphemistic) the world's oldest profession

(idiomatic) about this and that

a picture is worth a thousand words

the grass is always greener on the other side (the others' circumstances seem more desirable)

(idiomatic) to bite off more than one can chew

it's easier said than done