As stated, this amounts to a public order offence and is definitely something you should report. There may be CCTV available on his route, too. If you can remember which way he was travelling, what he looked like, what he was wearing, and any details about his bike, that would be useful for the police when they come to review any CCTV, as well as a fairly accurate time frame. You can also find your local neighbourhood policing team via the met website using your postcode - they may also be worth a shout in addition to 101.