Taking off, without clearance, ahead of cleared to land traffic is never a good idea.
 

On October 5, 2016, an Air Dolomiti ERJ-195, operating flight LH2993, (call-sign: Lufthansa 4TX) from Brussels to Munich, was instructed to line up and wait on runway 7R at Brussels. Having entered the runway at taxiway C6, the aircraft should have held at line up position 2, not far from the intersection of runways 7R and 01.

Tower: "Lufthansa 4 Tango X-Ray (LH 2293) Charlie six, line-up and wait runway 07 right.“
Tower: "Shamrock (Aer Lingus) 638, cleared to land 01, (wind reading).“
EI 638: "Cleared-to land 01, Shamrock 638.“

About 50 seconds later an aural alarm was heard in the tower indicating a conflict alert on the runway.

Tower: "Shamrock 638 Go-around Sir, go-around.“ (expletives deleted).
EI 638: "Going around.“
LH 2293: "Lufthansa 4 Tango X-Ray?“
Tower: (unintelligible). "Ah you were not cleared to take-off I’m sorry to say.“ (he's sorry).
Tower: "Yeah, you can continue now (the take-off) Sir.“

1 minute later............https://scontent-lhr3-1.xx.fbcdn.net...a1&oe=58956224

Tower: "Lufthansa 4 Tango X-Ray, contact departure now 126.625.“
LH 2293: "126.625 Lufthansa 4 Tango X-Ray, sorry for misunderstanding.“
Tower: "No problem, I just want to inform you that I have to write a report, (unintelligible) you do the same for your side.“
LH 2293: "Ja, we do the same, thank you very much.“

Air Dolomiti is an Italian regional airline with its head office in Dossobuono, Villafranca di Verona, Italy. It is a wholly owned subsidiary of Lufthansa.

Any ATC tapes for this online?

Edit: Found it.
https://www.youtube.com/watch?v=rWR9ucU9eUg

Think that impressed me about that audio exchange is the apparent very forgiving nature of the controller. There's a guy who realizes that simple errors (not misunderstandings) happen, and doesn't give the crew any tone about it at all.