Washing my brushes.
I cannot explain the disdain I have for this most mundane of chores. Maybe it's that it is the most mundane of chores. After a long day of painting, the last thing I ever want to do is clean up brushes. So I often don't. And that's bad. Oils dry slowly, so the next morning I can often swish them in mineral spirits and get back to work. But brushes start to pile up as the week goes on. If on day 3 I don't use a brush I used on day 1 or 2, by day 4 that brush may be toast. Sometimes, I have the good sense to at least rub some Walnut Oil into them each night, which generally keeps them soft for a day or two extra. But inevitably, I'll paint until the last moment before having to do something on a Friday, be busy all weekend, and wake up Monday with a taboret full of stiff brushes.
That's when I break out the brush cleaner whether I like it or not:
("Always washing!...Each brush is dirtier than a workman's collar!")