Has a lot to drink, because it's a party and he handles his liquor well. He is a bit nervous about being around Death Eaters, so he barely speaks to Bellatrix at all. She seems like she is in a bad mood. He talks some to Barty, maybe tells a few jokes. Tells a few stories.
He spends most of his time chatting with Heath, giving him a few knowing looks and talks about whatever comes up.
Lorcan relaxes a lot more as the night goes on.
If you want to talk to him, tag under this comment yo! I don't know play billiards or something. USE YOUR IMAGINATION!