Matching all words except one

Try:

\b(?!boy\b).*?\b

which means:

• Zero width word break (\b)
• That isn't followed by "boy" and another word break;
• followed by any characters in a non-greedy way;
• Up until another word break.

Note: the word break matches the start of the string, the end of the string and any transition from word (number, letter or underscore) to non-word character or vice versa.

If you use "boy" as splitter, you would get remaining parts. You could use those as selection keys.

>>> re.split("boy","I am a good buy and bad boy too")
['I am a good buy and bad ', ' too']

/\b(?!boy)\S+/g

You can use negative look behind:

\w+\b(?<!\bboy)

Or negative look ahead since not all support negative look behind

(?!boy\b)\b\w+

You can read about negative look ahead here