« Tout à fait »

From http://micmap.org/dicfro/search/dictionnaire-godefroy/fait, “a fait” already meant “absolutely” in ancient French.

« Je m’en fous »

It’s not “fous” as in “crazy” but rather the verb “foutre” (vulgar).
It’s vulgar for “Je m’en moque” (directly translated as “I’m laughing about it”)

« Fais gaffe »

From https://originedesmots.blogspot.fr/2014/02/gaffe.html:
“faire gaffre” means “keep guard” in ancient french

“tout à fait” can be translasted by absolutely, like “Be Chiller Too” Says.

“Je m’en fous” is pretty familiar. Think about a rough “I don’t care”

“Fais gaffe” is equal to “fais attention” but is much familliar. You may translate this by “be careful”