Before flippantly wiping out two of the UKs major cities (number 3 and 4 according to the technical measures and 2 and 4 according to other less.. official measures), perhaps those who are derisory might want to visit these places a few times with locals and actually see the sights, experience the people, and don't just go to the tourist spots.
I have been to London many times, if I go to the tourist areas I absolutely can't stand the place, when I go and visit my native friends and they take me out, I have a great time.
Manchester and Liverpool are both the same. They are culturally and historically very rich cities and while I recognise mancs and scousers have a reputation for being a bit rough, (and lets face it they aren't exactly the nicest of accents when they're really thick) , I have lived in Manchester city centre for 4 years now, and quite literally havent had a single jot of trouble. I am fully aware of areas I could go and it would be hell, but I simply avoid them (printworks...), as I now do in London.
Liverpool is really nice too, a really good example of how to modernise a city without losing sight of its past. Manchester isn't so great at that some of the time.
I really don't see how simply stating you hate 2 huge cities is in anyway constructive.
WRT. to Liverpool and going out, sorry I can't be of much help, it's been ages since I've been out around there for a night (says he of the non-constructive criticism!)