regex – hard string to match with regular expressoion

Can someone please give me an example of a string that would be very hard to match with a regular expression. then try to match it with a RegEx.

my input is a text file

my prior example I coded was
Write a piped command using grep, sort, uniq, tail, wc, and cut to read the provided data file and return the number of unique IP addresses that match the following criteria:
● IP address begins with 11
● Occurred before August 2018
● Occurred at an even numbered hour
● Has a size less than or equal to 100

cat lab0202.csv |cut -d” ” -f 1|sort -t”-” -k1 -k2 -k3 |tail -2 |head -1|sed ‘s/-///g’|wc -l