STAIRCASE: goes rapidly downhill

What better way to add credibility to a story about a bickering, middle aged gay couple than by casting two of the world's most notorious womanisers in the lead roles?
The logic behind the choice of Richard Burton and Rex Harrison escapes me but it makes for interesting watching - at least for the first 10 minutes.

After those first few minutes it becomes obvious that they have no idea how to convincingly portray a homosexual man as a real flesh and blood individual and have chosen to fall back on the old stereotypes instead. Harrison adopts the cliched 'sucking a lemon' frozen facial expression and flouncy hand movements, while Burton goes for a bitchy coalminer characterisation. The result is a pair of caricatures more likely to be found propping up the bill in a gay drag revue than actually existing in a real world community.
Charlie (Harrison) and Harry (Burton) have been a couple for more than 20 years, living above Harry's barber shop in some ill-defined part of London. They bicker and derive perverse pleasure in pushing one another's buttons even though they recognise that it threatens the stability of their relationship. Harry's inferiority complex is complicated by the stress of caring for his invalid, bedridden mother (Cathleen Nesbitt) who lives with them and requires constant attention.
Miscasting the lead actors would be enough to sink most films on it's own, but director Stanley Donen is determined to send STAIRCASE plummeting into undersea crevices so deep that even remotely controlled robot submarines can't reach them. There's no other way to account for the atrociously overblown dialogue spouted by his two implausible characters. The script, by Charles Dyer and based on his own stage play of the same name, makes absolutely no allowances for the fact that the theatre and cinema are different mediums. What works on stage where actors must ensure the back row of the audience can hear them and see the emotion being expressed comes across as hammy, overheated and overly theatrical on the big screen.
Burton was no stranger to cinematic disasters in the late 60s and early 70s (and this wasn't the last time he'd play a gay character) but 1969's STAIRCASE is particularly dreadful because it has no redeeming qualities - no camp value, no so-bad-it's-good performances and no memorable dialogue. It's just awful.