Yet another potential minefield for the modern Gentleman is the issue is whether to hold a door open for a lady or not.
Essentially, most people would still consider it mannerly for a gentleman to hold a door open for a lady, but there are a few people out there who would consider this to be based on the sexist notion that the female sex is weaker, and therefore doing so implies that the lady is unable to hold her own door open.
I would suggest that the best rule and the way to avoid any suggestion of sexism is not to limit yourself to holding doors open only for ladies, but for other gentlemen as well. That way your mannerly act be justified as gender non-specific, and remains squarely in the realms of politeness.
As with so many gentlemanly ways this does require you to take a little extra time in your day and in the same way as a gentleman would hold a door open. He should also expect to make himself available to offer assistance in other ways; lifting pushchairs and buggies, helping with luggage. Anyone travelling with children will have their hands full and the perfect gentleman should be alert to the possibility that his assistance may be required, and he should be prepared to make himself available should the need arise.
It may take a little time out of your day but it’s good for the soul!