Max Verstappen branded Lewis Hamilton a "stupid idiot" and gave the seven-time F1 champion the middle finger following a practice skirmish ahead of the United States Grand Prix.
The title-chasing duo, who head into Sunday's race separated by six points in the drivers' standings with six races remaining in the season, have been involved in a number of high-profile on-track incidents this season.
The latest was minor under the circumstances but underlined the needle that exists between them as they fight for the crown, with Verstappen aiming for his first title and Hamilton a record-breaking eighth.
Just 10 minutes into the second session at the Circuit of the Americas, and at the end of a lap going into the final corner, Hamilton dived down the inside of the Dutch driver, forcing him to run wide.
On Verstappen's return to the track, the duo then went wheel to wheel down the start-finish straight and into the uphill first turn.
As Verstappen eased off, he gave Hamilton the middle-finger salute and described him as a "stupid idiot" over the team radio, to which he was told to "just ignore it".
Assessing the incident, team principal Christian Horner said: "They were queueing up to start the lap and Lewis decided to jump Max."
With regard to the middle finger, Horner joked: "Max was just pointing out he was first in the queue, so one of those things."
Verstappen later became agitated with traffic and aborted his final soft-tyre run to end the session eighth on the timesheet, 0.878secs behind the leading time of 1:34.946s set by Red Bull team-mate Sergio Perez.
Perez's time, though, was a tenth of a second adrift of the best of the day posted by Mercedes' Valtteri Bottas during the first session when the team was dominant.
Hamilton had to settle for the third quickest lap in FP2, 0.364s behind Perez, with the Briton separated from the Mexican by McLaren's Lando Norris.
At one stage on the soft tyre runs Hamilton was momentarily top of the timesheet with the quickest lap of the day of 1:34.842s, only for that to be deleted for exceeding track limits at turn 19.
Bottas, who will serve a five-place penalty for the race for his sixth engine change of the season, was fourth in FP2, four-tenths of a second behind Perez.
McLaren's Daniel Ricciardo, Lance Stroll in his Aston Martin and Ferrari's Charles Leclerc then separated Bottas from Verstappen, with the second Ferrari of Carlos Sainz 0.973s back.
That was close to the same time gap that split Bottas from Verstappen in FP1 such was Mercedes' superiority in that session.
On long-run pace, however, Red Bull at least offered up hope there might be a race as it matched Mercedes.
As in FP1, Alfa Romeo's Antonio Giovinazzi was again 10th quickest, 1.192s adrift, followed by Alpine duo Esteban Ocon and Fernando Alonso sandwiching AlphaTauri's Pierre Gasly.
Alonso blotted his copybook late on, though, with a spin out of turn 19, locking up and hitting the barriers with the rear of his car.
Also as in FP1, Haas' Nikita Mazepin was slowest, finishing three seconds down on Perez, and half-a-second behind the driver in 19th in Williams' George Russell.
The Briton will start the race at the back of the grid alongside Sebastian Vettel in his Aston Martin as both have new taken on new power unit components.
United States Grand Prix second practice times
1. Sergio Perez [Red Bull] 1:34.946
2. Lando Norris [McLaren] +0.257
3. Lewis Hamilton [Mercedes] +0.364
4. Valtteri Bottas [Mercedes] +0.414
5. Daniel Ricciardo [McLaren] +0.511
6. Lance Stroll [Aston Martin] +0.615
7. Charles Leclerc [Ferrari] +0.626
8. Max Verstappen [Red Bull] +0.878
9. Carlos Sainz [Ferrari] +0.973
10. Antonio Giovinazzi [Alfa Romeo] +1.192
11. Esteban Ocon [Alpine] +1.212
12. Pierre Gasly [AlphaTauri] +1.296
13. Fernando Alonso [Alpine] +1.430
14. Kimi Raikkonen [Alfa Romeo] +1.612
15. Sebastian Vettel [Aston Martin] +1.772
16. Yuki Tsunoda [AlphaTauri] +2.037
17. Mick Schumacher [Haas] +2.095
18. Nicholas Latifi [Williams] +2.308
19. George Russell [Williams] +2.544
20. Nikita Mazepin [Haas] +3.080
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