Did Tony really like to party?
We'll list every party we know Tony has attended in the MCU (including deleted scenes and What If? S2 E4, since that Tony is a copy of the main Tony from the MCU) and see what he was doing there.
When Tony was 17-18 he went to parties with other MIT students. Here's the main post, but I'll quote the MIT alumni again:
“I remember him at after-parties on Thayer Street. He was up later than anyone else. But you could always get a ride home with him, because he always had a car.”
“No one really knew him, he was just a rich kid. Everyone wanted him around, though, because he'd always bring something fun for the party.”
What he was doing there: entertaining others. Didn't really communicate with them, didn't drink, helped them get home.
Bern (New Year Eve, 1999)
Two questions: 1) Does he look drunk? 2) Does he willingly communicate with people other than Maya and Happy? My answer to both questions is no.
What he was doing there: separately from everyone else quietly communicated with Maya; avoided people except her, to help with this task took Happy with him; if it was not possible to avoid interactions, reduced them to a minimum; despite Yinsen's words from IM1 he didn't seem drunk, while people around were; happily left the party to spend time alone with Maya. Wearing sunglasses in darkened rooms at night.
Jet (on the way to Afghanistan, 2008)
What he was doing there: sprawled on the couch, sipping champagne and looking at his flight attendants, while drunken Rhodey tried to convince him that he's a good person. The party didn't last long - one of the flight attendants blindfolded him and took him to the bedroom.
Dubai (2008, alternative trip to Gulmira)
As you can see it was either a VERY fun party or not at all.
What he was doing there: creating an alibi for himself to fly to Gulmira to save people from the Ten Rings. Wearing sunglasses at night. Avoiding interactions, visibly uncomfortable with those he couldn't avoid. Left immediately with two girls ordered for conspiracy. Having reached the bedroom, left them and flew away on the mission.
P.S. He also asked a third girl to join them on the way to the bedroom, leaving the guy who was with her alone. I imagine that incident potentially could create another Marvel villain.
What he was doing there: showing the public and the board of directors that he's fine. Avoiding people, had unwanted interactions with Coulson and Christine just because they caught him. Basically ignoring Coulson, staring at Pepper. Drank a little. Enjoyed time only with Pepper: slow dancing with her, joking around, paying attention to her feelings and needs, asking if he makes her uncomfortable, and offering to go outside for some fresh air when she needs it. Together with Pepper, left for a secluded place on the balcony. Quietly talking to her there. Went to get drinks for Pepper without question when she felt the urge. Told Christina that he is feeling uncomfortable there. Actually showed signs of discomfort. Immediately left after talking with Stane.
Another super fun alibi party. This time to "pass" the armor to Rhodey and push everyone away from himself so that he can die alone and so that no one will mourn for him.
What he was doing there: acting. Pretending he is dead drunk and enjoying the party. Wearing sunglasses at night inside the house (in the deleted scene with Natasha). Destroyed the ice statue of himself. To Natasha's question "What about those people around?" said "That's why we are doing it. It's for them. It's my party, it's my friends. They like this sort of garbage". What kind of "friends" are these for him, you can find out from Jon Favreau himself here. Kicks everyone out of the house by yelling during the fight with Rhodey. Just lying exhausted in a destroyed house after everyone left.
What he was doing there: greeted Rhodey and Sam. Spent some time in the small company of Thor, Maria Hill and Rhodes. Was quiet - listened and smiled more than he spoke. Drank a little, perhaps less than the others. Quietly played cards with the team after most people had left. Became active only at the stage of attempting to lift the hammer. Encouraged others to try.
To summarize: he was quiet and attentive overall. Was just hanging around his house like a stranger while people other than the Avengers were at a party. Seemingly felt more comfortable when most of the people left and he stayed with the team, just playing cards and drinking beer.
Indian wedding (Spider-Man Homecoming)
What he was doing there: Tony attended someone's wedding in India. Apparently he didn't know the language, so he couldn't communicate and kept away from other people. Looked busy with Peter and something else. Showed no interest in the event. Didn't really drink and left quickly.
Grandmaster's Birthday (What If?)
"I've put my party days behind me".
What he was doing there: Grandmaster forced Tony to stay to celebrate his birthday by threatening him with his Melt Stick. Tony settled on the couch away from the others and was not very pleased when the Grandmaster joined him. Showed no signs of enjoyment throughout the event. Just wanted to get home pronto. Chose to save the people first instead.
Victory Celebration with Val and Korg (What If?)
What he was doing there: enjoyed their little company, but thought about Pepper and Earth.
As you can see, the common characteristics of all or most of his party visits, except those when he was in a small group of close friends, were:
sunglasses (if available) when they don't make much sense except covering his eyes from others
focusing on quiet calm interactions with people he knows
leaving the parties at the first opportunity/running away from them
focus on entertaining others, not himself
no alcohol consumption or consumption in small quantities
showing signs of discomfort
looking and acting like he is out of place
At the same time, at quiet parties with a small group of close people, he seemed to feel more comfortable.
You can already draw your conclusion. Mine - he didn't like parties at all. He sometimes enjoyed spending time in the company of people he liked, and it had nothing to do with enjoying parties per se.