Florence - it is an easy habit to fall into for anyone, man or woman. This thread is almost the male version of the recent thread on avoiding looking 'Mummsy'. I have to admit it easy for Dads to also start to look quite 'Daddsy' after kids arrive and there are various grades of male grungeiness within that overall Daddsy look.
What does DH do for a living? Does he work at home or say in a job that requires fairly informal dress that is say a driving job or even an office job that allows dress down? I used to work with city tader on huge salaries that dressed down in the office just as you descibe your husband. Some looked like they had slept in their clothes or just been sunbathing in the garden in grungy shorts.
Has DH had a sudden redundancy or big life change or an illness? I became, a SAHD/WAHD and then very ill and it did set me off down this track but I realised I had to totally rethink my wardrobe.
I do not think it is right to just chuck out DH's clothes or decide to buy him new ones without his agreement though. He has to make that decision himself.
What I did was talk to DW about what she liked me wearing (she and I have always liked nice clothes) and I also told her what I liked her wearing. We listened to each other also thought about our lifestyle together and then threw out most of our old summer clothes last summer and bought new ones for holiday and home casual wear. We also just threw out most of our old winter clothes and will buy new ones in the Autumn.
We kept a few of the newer things and some slightly older things for gardening and dirty jobs and but apart from that everything went. We then tried to think of different situations where we need different types of clothing. Formal occassions, going out into town, working at home, visiting friends, holidays, wet and foul weather. We then worked out what full outfits and individual items we really needed. That way we felt we would not waste money or time buying stuff we did not need or would not wear.
The motivator to me, apart from my own general unhappiness about how I looked, was that DW responded to what I had said to her and so I felt I owed it to her to look nicer too. Making it a joint project about our lifestyle and shopping together made it more fun.
Might that work for you and DH?