Those pictures released this week of David and Victoria Beckham on the dance floor at their eldest son' s 21st - David gripping a glass in one hand, Victoria's leather-clad bottom in the other - reminded us of the perils of mixed-generation parties.
The Beckhams weren't sharing the party with Brooklyn, but these days parents with birthdays ending in 0 often do share a party with a child turning 21. It makes perfect sense: you're putting up the tent, why not make the most of it, you love all your children's friends …but stop right there.
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In the 21st century, the people most likely to cause embarrassment, drink too much, have sex with someone they shouldn't – possibly around the back of the marquee – accidentally set fire to their sleeve, trip over a cable and knock out the lights, get into a fight about politics or the environment - are the older generation.
While the 20-somethings are oohing and aahing about the amazing floral place decorations, cramming into the photobooth, toying with their espresso martinis and instagramming everything, it's the parents who are really letting their hair down, because this could be the last big party they ever throw – although they've been saying that since the millennium.
Anyway. For all the parents planning a mixed bash in the year to come, here's a quick reminder of things not to do at your son's/daughter's 21st.
Make lots of personal comments to the younger guests.
Women especially have a habit now of behaving with young adults as we do with babies: we can't get over how delightful they are, we want to squeeze them and tell them how pretty they are, and while a straightforward compliment is fine (eg great shoes) obsessing about the length of a 20-something's legs ("Look At Your Legs! They Don't Stop! Look") or how dazzling they are ("So Handsome! Like the Young David Essex…OMG!") and so forth can get a bit too much.
Dance like no-one is watching.
Your friends will think it's hilarious and get on with doing their own Bobby Farrell impression but it's distressing for the younger crowd.
I.e., weave around, waving and pointing, trying to bum cigarettes (no-one smokes), occasionally striking up a conversation about the weather or how boiling hot you are.
Grab the mic and make an impromptu speech
The older we get the more comfortable we are with the sound of our own voices when alcohol has been taken and, at a mixed gen party, there is unlimited scope for the 'You might not believe it but when we were your age' stories. No.
Talk to the young people about their jobs or why they're single
Hassle the DJ
You may well become convinced you can get this party started, plus you want a tune with lyrics. Doesn't everyone! The DJ hasn't heard of Shame Shame Shame by Shirley and Co, he doesn't want you to hum it, he, he doesn't need help rifling through his vinyl just in case he's got some Labelle/ Bronkski Beat. He can't hear what you're saying because he has headphones clamped on and he's been warned not to remove them.
Drink more than one espresso martini
Think you might just have a quick lie down
Take your shoes off
Take anything off. Decide you can do ceroc and you really want to do it with someone in particular who also has no clue.
Insist on staying to the bitter end as you would do at a regular older people's party
The idea is that at some point the grown-ups will give way to the younger generation, yield the floor, step away from the DJ booth. So when your partner says "Think it's time to leave them to it" giving you the special wide eyes and head jab then, just this once, go along with it.