Thanks for your help! I WAS mutating the input.
Silly me!

No. I am questioning the expected result, it's clearly wrong on more than one of the random tests:
25
25
25
10
4
8
25
2
25
6
3
{ tim: 'pissing_about',
jim: 'pissing_about',
randy: 'pissing_about',
sandy: 'canteen',
andy: 'cleaning',
katie: 'IS',
laura: 'pissing_about',
saajid: 'finance',
alex: 'pissing_about',
john: 'trading',
mr: 'regulation' }
It should work for random inputs too - Expected: 'kill me now', instead got: 'party time!!'

The input has 5 "pissing about"'s and would clearly be over 100 (Party Time), but it's expecting "kill me now"

In JavaScript, the random tests appear to be broken.
1
10
5
10
10
3
8
10
10
25
10
==102
{ tim: 'accounts',
jim: 'canteen',
randy: 'retail',
sandy: 'canteen',
andy: 'canteen',
katie: 'regulation',
laura: 'IS',
saajid: 'canteen',
alex: 'canteen',
john: 'pissing_about',
mr: 'canteen' }
It should work for random inputs too - Expected: 'kill me now', instead got: 'party time!!'

It's expecting result for <=80