Unfortunately, you'll have to clink this link to find out, but I promise promise promise you that it's a good one.
This strip is mainly linked in my mind with the 2001 D12 hit "Blue and Yellow Purple Pills", I think mostly because the dog in the strip strongly resembles Bizarre, but blue, and in dog form.
I was never sure about this link, but chronologically, it makes sense, as it was published in July of 2001, when the D12 album was quite popular. Thematically, it makes sense because, well, look at the title panel. So what I'm saying is that Jim Davis was at least aware of the drugged-up antics of D12 in 2001.
I'd also like to say that, even though I can't steal images from their site, the Garfield Comic Strip Archive is really amazing at finding what you want... particularly if what you happen to want is a very specific and weird strip from the early 2Ks.
After further investigation, it appears that Bizarre actually wears almost the same hat during his verse. Just go to 3:15. Also, when he finishes the verse by yelling, sorta Hulk-style, "Bizarre here all night!" it's the exact voice that I hear from old "Tree Dog" in the Garfield strip. The proof, as they say, is in the pudding.