How often have you heard this advice on the golf course? Ask Gary or any teaching professional golfer if it is good advice and the answer is no it is not! While generally well intentioned, the Rules do not permit a player to give advice to anyone in the competition playing on the course other than to a partner nor to ask for advice from anyone other than from a partner or either of their caddies.
What is advice? It is any counsel or suggestion that could influence a player in determining his/her play, choice of a club or the method of making a stroke. Suggesting that you ‘keep your head down’ comes into the category of ‘the method of making a stroke’. So, while playing in a competition making ‘helpful’ suggestions to your fellow competitor when they are having a bad day is against the Rules! What are you permitted to ask or give information about? Information on the Rules, distance or matters of public information such as the position of hazards or the flagstick on the green is not advice. By all means during practice rounds give each other advice or make suggestions as to how to play a shot but in practice only and not while playing in a competition.
See Definition of Advice, p22 and Rule 8 Advice; Indicating Line of Play p55 of the Rule Book