Inspired by the commuting thread. We need a number, ideally a short description of the route and why you hate it. Possibly London-centric but all welcome!
Mine is the 43 (London Bridge-Friern Barnet) because the Holloway Rd section takes FOREVER and it’s a pain to get late at night because it takes ages to turn up and is then packed full of dicks. Also always swaps drivers mid journey.
25 (central London to East London) - probably the bus I’ve had to abandon the most mid route to vomit
838 (Cannock to Stafford) - infrequent, never appeared as timetable and would sometimes divert through Penkridge which was useless for me