Steve is grilling out for his friends in Dr. Selvig's backyard

Loki doesn't appreciate being left out so he decides to make the party more 'fun'

Bucky and Natasha arrive and proceed to do some drinking and cuddling

Thor and Jane make a connection and Thor makes a confession

Namor arrives and greets Steve

Tony arrives with an entourage of professional ladies, caterers, a band and the ego to go with it.  Please save us Pepper.

Thor runs into Bucky and Natasha and Steve shows up to say hi.

Namor decides that he wants to assert his alpha-maleness and introduce himself to Jane.

Tony runs into Thor at the bar.

By the time Thor slips away from the conversation to offer Steve a better chance to reconnect with his old friend, and just as he simultaneously dispatches the last bit of food on his tray, the party is in full swing. The band is playing something he recognizes vaguely from the television (Loud and energetic enough to aggravate Rogers, which was most likely Stark's plan from the start.) and what started as a quaint little gathering of friends has turned into a spectacle worthy of the local paper. He is starstruck, distracted and awed by a celebration of lights and sounds unlike anything he's seen before, and he wanders aimlessly through the crowd to catch every second of it. 

In fact, he almost forgets why he'd left Jane in the first place until he spots the fully stocked bar. He's half-tempted to help himself, but he knows by now it's customary to wait and be served. One arm clasped over his chest, the other resting atop it as he scratches his beard, Thor attempts to consider the available selection. 

Tony and Pepper board the jet without any bells and whistles in tow, if only because he knows she’ll try to talk him out of it; he’d rather save that argument for the afterparty, when they’re (hopefully) both good and tanked.

Steve asked for a low-key get-together, and Tony’s willing to acknowledge the guy’s Cap-tacular modesty. But unfortunately for Mr. America, his friend is convinced he doesn’t have his own best interests at heart.

They pull up in their rental just ahead of the trucks he’s ordered in from Santa Fe, and like Namor, he’s probably a tad overdressed for the barbeque Steve had in mind.

Out of the trucks pour a slew of caterers, tables, and crates filled with an assortment of hard liquor and two full sets of Perrier-Jouet Champagne. Before Pepper can muster more than a skin-splitting glare, Tony breaks away to have a quick word with the captain of the swelling banquet brigade, then skips on over to Steve at the grill, his arms outstretched.

Scrying orbs float above their pedestals in this room of Loki's chambers, showing him all manner of images from across the nine realms.  Some of the orbs keep watch over Asgard; some over the wretched jotun and the scheming dark elves.  But Loki's gaze is fixed on the scenes playing out in Midgard: Thor and his friends have gathered for an event, a Midgardian holiday celebrating the birth of the country that serves as Thor's prison, and Loki does not appreciate the lack of an invitation.  He watches the interactions flash across the orb's surface with a rising restlessness; his mind considers and calculates and fits ideas together rapidly until the thought process coheres into a decision.

It is late in Asgard--he has answered the petitions for the day and seen to the realm's continued security.  The pieces of his other plans remain in place, moving at the expected speed and toward their proper ends.  He has time for fun.

When Loki arrives in Dr. Selvig's backyard, he is cloaked not only from Heimdall's omniscient sight but also from the guests that mill around him.  They talk and laugh with one another, ignorant of his presence as he moves among them; he is a ghost, with no more tangibility than a breeze that toys with their hair.  Loki sneers at Thor, clasping Jane's hand and looking pathetically earnest.  He has little regard for Steve Rogers, either, standing around with a well-dressed, sharp-eared man and looking just as stern and humorless as Loki imagined he would be.

There's a table set up with food and drinks, and most of these people have availed themselves of the refreshments.  Loki's mouth melts into a grin as he dips his fingers in the punch bowl; the liquid flows up his hand like tributaries seeking an ocean, and he manipulates the composition, altering it, improving it.  Once done, he lets the newly imbued punch spill back into the bowl, then focuses his attention on the other offerings.  Steve has provided water, soda, beer and so forth; all of these Loki attends to in turn.  He whispers to the moisture in the wind, and enchanted droplets collect on all the bottles, all the cans; they shimmer briefly, invisibly, as they sink into their targets.