Glasgow overcame a Leinster side that had dominated recent encounters between the teams. The Irish province had won six of the last seven meetings, including a heavy 52-0 victory in last season's Champions Cup quarter-final in Dublin.
This time, however, Glasgow were firmly in control, sealing a 38-17 win in front of their home crowd.
The flashpoint came when Hastings exchanged words with Leinster fly-half Sam Prendergast and ruffled his hair, sparking a reaction from players on both sides.
Both Hastings and Leinster prop Rabah Slimani were shown yellow cards for their involvement. Despite that, the Glasgow stand-off appeared unfazed, leaving the field smiling, waving to supporters, and soaking in the applause.
After the match, Hastings played down the incident and joked about how his coach, Franco Smith, might respond.
"I don't know. Franco's a pretty angry guy so we'll wait and see. No, I'm joking."
He then explained the build-up to the altercation. "It's a bit of back and forth. It's always been like that. You know what they are like in these games, then the fight went off. It went on for a bit too long. They pulled Gus [Angus Fraser] back so I thought I'd got away with it.
"But, look, I'll take my discipline. A bit silly.
"It means so much to us, these games. We've been on the wrong end of a few of these results and I think that's maybe why it spilled over at the end. You can see how much it means to both teams.
"I thought espcially in the first half the boys played unbelievable. Obviously Leinster were going to throw it about when they were down and I thought we dealt with that pretty well. We know they are a very dangerous team as well so if we meet them later on in the year it will be tough."