Thickest I've seen in real life is a local guy I've hooked up with several times. Big cock, probably 9 long, I'm 8 long 5.5 around, based on that I'd guess his cock is 6.5 around at the base and head but bulges to much more in the middle, so fucking thick can't wrap my hand around it and I have big hands. He's never fucked me but I've enjoyed getting my mouth around that beauty and swallowing his loads.