Ok. He hit you. He had a bad time with 5yos hitting him and it made him feel angry, having toddlers reduce him to a tot himself. So when they left, he took it out on you. He gave him some control back. He was reduced of his power for a while. Now he has regained it. He's hurt someone else. Does this remind you of anything? It reminds me of nursery school children, when they hit other random kids because they've been hit themselves.
If you take it and do not retaliate, then he'll know that it's ok to do it again.
It might just be this once, or it was because he felt x y and z, but mark my words, he'll do it again, because now he knows he can, and get away with it. Obviously it's your fault, for having the tea, for not dealing with the kids. Obviously.
This is a stark warning for you. If you let him get away with it now, he'll do it again, you know he will, deep down you DO know that. If you stamp on it now, if you regain control, if you fight back, he'll know that he can't just lash out. He has to find another way of dealing with that feeling of losing control. He has to be grown-up for once. Is that so bad? He has to take responsibility for his own feelings. Why are men so bad at this?
You choose. You brush it under the carpet, give him a harsh word, and hope he doesn't do it again (whilst living in fear that he will, knowing that he will) or you put a stop to it now.
Toddlers. They hit and you tell them that it is not right. You don't say "well you hit so and so because they made you feel frustated", you tell them that under no circumstances is it ever right to hit, anyone. Men = toddlers. You need to set the record straight. It saddens me that tots are now taught to hit rather than be bullied. That's just saying "it's ok to hit if you feel angry honey!" - NO IT ISN'T!
He's a man now, he should deal with his anger better. If he can't, then that's his problem, not yours.
He Is The One With The Problem Not You.
This is unacceptable and it's about time he grew the fuck up and learnt how to deal with frustating situations. Otherwise, how is he going to cope when they get older and start challenging his authority? Who will he hit then?