Oh what an idiot. So he pays less rent. Does this mean he only uses the kitchen and/or bathroom only 80% of the time (ie. 4 days of 5 days of the week). I suspect his showers are just as long as everyone elses. You are discussing common areas, which are used (or at least available to use) and maintained equally by all.
Get yourselves organized (you other 4). Then, make a list of 5 jobs that need doing around the house like Lahnna suggests. Write it out. Likewise, make the table of shared items and who buys what, per Lovesjoy's suggestion.
(I had housemates as a student and we did both those things--we got along really well b/c of it, especially the repayment amount b/c some people really couldn't shop as often as others)
Make a note for him with this agenda and your next meeting date on all this. Say that if he doesn't have time he should let you know in writing which of the jobs he prefers. If he doesn't get back to you, he gets what's left.
If he goes completely passive-aggressive, I would let your landlord know you don't want this person renewing in August. Tell him/her you have a system for maintaining the house (show them!) they he isn't respecting. Say that you are all prepared to leave. Your landlord will agree it is MUCH easier to find one new tenant than 4. Especially tenants that are keen to keep the place clean.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh