A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

part of the training for pilots: Touch and goes proved fairly
simple; power on, flaps up produced almost spontaneous
response with a short ground roll.
touch something • touch upon something
touch something —
1
. put the hand or finger upon smth. so
as to feel it: As his hand touched the surface of the mirror, it
rippled like the water in a pond. He drew his hand back, star-
tled. 2. (cause to) be in contact with smth.: Scientific infor-
mation on the Martian atmosphere was gathered even before
the Landers touched the surface. 3. have to do with smth.: I
still find it hard to believe teachers would come to workshops
and refuse to touch the computers.
touch upon something —mention smth. briefly, casually, or
in passing: Himes succeeded in treating more extensively and
intensively themes he had only touched upon in his first book.
tough cookie • tough cookies
tough cookie —(sl.) an unyielding person who is difficult to
deal with: He’s a real tough cookie and you know it.
tough cookies —(sl., parenthetical) too bad; very unfortunate
(also: tough bananas): If you give the wrong answer, well, tough
cookies, you have to move backward.
tough nut to crack • tough row to hoe
tough nut to crack —(also: hard nut to crack) 
1
. a difficult per-
son to deal with: Meggie was going to be a tough nut to crack
and he couldn’t afford to frighten her. 2. a difficult problem
or task to undertake: Getting them all here on time will be a
tough nut to crack.
tough row to hoe —(also: hard row to hoe) = tough nut to crack
2: Getting the contract signed is going to be a tough row to
hoe.
Note: 
Neither expression correlates in meaning with the phrase
tough act to follow
—(also: hard act to follow) used of an out-
standing individual or a particularly good performance that will
be difficult to emulate: The gifts, the decorations, the food —
everything was exacting and amazing. It will be a tough act
to follow.