Names will get me, too. On The Hour is full of really funny names but the juxtaposition makes ones like Dawn Sentinel much funnier when the rest of them (Hilliard Halliard, Peter Sisters Christmas etc) are so much more obviously designed to be funny.
Another tiny moment that had me howling the other day is when Partridge doesn't want Pete Durant to see his book stall at the train station, so he rushes up to intercept him and turns him around with a handshake, saying something like "I hope you don't mind if I just turn you around like that", and Pete replies "no, not at all". Both sides of that exchange just crippled me. Pete's matter-of-fact replies to everything are in fact very funny. He gives a very funny memorable performance even though he's essentially another straight person for Alan to interact with (like the Crash Bang Wallop woman or the tax inspectresses).