Slag off

I found a really good relationship advice site that is obviously written by a Brit, because there are various phrases that I never hear in the US.

I was reading an interesting blog post over there, and came upon the phrase "slag off", which I've never used. According to Using English (a good resource for ESL teachers and learners), it means "criticize heavily", as in "I slagged her brochure off because the design was awful."

Maybe I should start using that phrase to see people's perplexed reactions :D