I am with Hvert on this - if you let it slide (and I am a great one for letting things slide) the bustards become emboldened. In any case sometimes, often times even, they are not bustards and have just been thoughtless and a mild check is all that is needed.

Now if the unacceptable behaviour continues, you will have to fall back on your contract of employment, job description, performance review, company grievance policy and such legal employment protection rights as exist in your region. Firm but civil often wins the day.

'Excuse me' is good - I am going to practise.