The diner
Justin's trick from the party shows up to see him...he's brought flowers. Oh no... see Justin, this is why you don't pick up virgins!!
Justin takes a minute to go talk to the guy... he snaps at him from the beginning, but I think he's irritated more with himself than anything because of his decision to kiss him. He's realized in the light of day that he technically broke the rules he set up (though I don't personally see it as that major an infraction, considering the circumstances) and hurt Brian, not to mention given this guy false hope. It's just a bad situation for everyone involved.
So he borrows a move from the Kinney playbook and gives a similar speech to the one Brian gave him to get rid of the kid. Only somehow, perhaps because of the different circumstances and Justin's real frustration here, it sounds a bit meaner to me. Justin you are not good at being an asshole! Please never do it again. You just broke that kid's heart. I much prefer you when you are sweet.