Crowley could sense that Hastur was present from the moment he arrived. It's that feeling you get when you're walking past a clogged drain on a dreary, rainy day (the type of rainy day when you have to go somewhere and it's just too rainy to be atmospheric) and there's something stuck to the bottom of your shoe and you're not sure if it's a wet leaf or wet dog poop-- and you look over and see the slow spiral of muck that's trying to go down the drain and see some indeterminate object that makes you gag just slightly... yeah, that feeling. He's been avoiding him.

So clearly, a couple of hours later, he rounds a corner and runs smack dab into him. "Oh. Hey," he says, eloquently.