One of the few things Wyll mentions about his past is that when he was fourteen he got so drunk he puked in Dillard Portyr's bushes. This is meant to be just a funny throwaway line, that's it.
First, Dillard Portyr is a Duke of Baldur's Gate. In fact, Portyr is one of the longest running Dukes of Baldur's Gate (for some strange reason Dukes tend to die often under horrible and/or mysterious circumstances in Baldur's Gate). Portyr was Grand Duke before Ulder Ravengard, until (for some inexplicable reason) he abdicated that position. So any party Wyll is attending at the Portyr's house is probably for good reason.
But surely there's no important event that occurred when Wyll was fourteen that we know of—
Just kidding, there absolutely is. Arguably one of, if not the most important event of Wyll's childhood.
You see, Wyll would have been around fourteen when his father, Ulder Ravengard, was elected to Duke.
An election that only happened because the prior head of the Flaming Fist—Abdel Adrian—was assassinated.
Now Abdel Adrian was a beloved member of Baldur's Gate. He was a retired adventurer, who had gone on to lead the Flaming Fist and then become Duke. One of his nicknames is literally The Hero of Baldur's Gate. As Blaze of the Flaming Fist, Ulder Ravengard was his second in command. There is no world in which Abdel Adrian and Wyll are not familiar with one another. It is likely that they were close and probable that Wyll regarded him as one of his personal heroes. And then Abdel Adrian was assassinated on returning day in 1482 DR, in front of a large crowd of Baldurians. Except assassinated isn't quite right. You see Abdel Adrian was a Bhaalspawn, overcoming his parentage to become a hero of Baldur's Gate. Bhaalspawns are compelled to seek out other spawn destroy them and it was a fellow Bhaalspawn who attacked him. Eventually one of them emerged victorious from the fight but we do not know which one. The other turned into a Bhaalspawn Slayer and attacked the crowd before eventually being slain by the Flaming Fist and a nearby group of Adventurers.
Wyll was almost certainly in said crowd on that day. His father would have most likely ushered him away, perhaps into the care of someone he trusted, before going to join the fight himself. Many people were killed in the ensuing fight, including many of the Flaming Fist. It is very likely Wyll knew several of the people who died, he definitely knew Abdel Adrian.
And there would be no time to mourn. As soon as Abdel Adrian's death was confirmed, Ulder Ravengard would be acting Marshall of the Flaming Fist and on his way to being voted in as Duke. Suddenly everyone and anyone would be interested in getting to know Wyll, pegging him as an easy ticket to get at his father. And meanwhile Wyll is suffering the loss of some of the most important people in his life.
Likely a celebration would be held in honor of his father's new position. It would make sense for it to be held by the Portyrs. And then Wyll is suddenly thrust into a celebration with little supervision, his father being dragged off to play politics. And so maybe he has a little too much to drink, because everyone wants to talk to him and Wyll just wants to mourn in peace.
And in the end he throws up in Dillard Portyr's bushes. And now, years later, Wyll plays it off for laughs. It's funny, really, when you think about it. His father's big day and Wyll's just off puking in the bushes.
Wyll is always playing his suffering off for laughs.
Maybe it's a silly throwaway line.
