This is actually an encouraged practice in Islam. Allaah (swt) has prescribed for His Prophet (peace and blessings of Allaah be upon him) and his Ummah the Sunan al-Fitrah (practices that are in accordance with the natural inclinations of man):

The Prophet (peace and blessings of Allaah be upon him) said: “Five things are part of the fitrah: circumcision, removing the pubic hair, trimming the moustache, cutting the nails, and plucking the armpit hair.” (Reported by al-Bukhaari, 5441)

For further information, you can see:

http://www.islamqa.com/en/ref/2887
http://www.islamqa.com/en/ref/9028

This kind of information might also be a good basis on which to tell the person. You could inform them of this practice in Islam and they might appreciate the need to act without being told directly.