This depends a lot on where you are. I've lived in York, Darlington, Leeds, London, Oxford, and Liverpool for decent periods and used buses in all of them regularly. Only Darlington was really unpleasant for buses - they were often every half an hour and if one came early and you missed it you would be left in the cold for ages without information.

Oxford was great (though cycling was even better); Leeds, Liverpool, and York were perfectly fine, with regular and reliable services; London's are famously efficient.

Antisocial behaviour isn't honestly that common in my experience, though I'm sure that varies by location. Had some aggro in London once, and again on a London night bus. The football special to the LNER stadium in York was properly boisterous, and quite threatening to the poor away-supporting family on the lower deck, but that at least carried a copper to make sure nothing stupid happened. Other than that, I've only ever really seen loud schoolchildren - who can be annoying but have never caused difficulty for anyone outside their group. I've honestly seen worse behaviour on the tube (and been the object of it on Cross Country Trains).