Slightly lower nose attitude to accellerate to V2 or V2 +10kn. If that doesn't work then it's time to use up some of that engine life that engineers keep going on about (only joking, F.E.s)
If the aircraft has all engines running and does not achieve V2 following a normal rotation then something's wrong: windshear, heavier than planned, power down, gear left down
Yes, it's unsafe inasmuch as flight tested margins are being eroded and, in the event of an engine failure, you could lose further speed and be in a high drag situation, closer to Vs, stall in a turn and also be approaching Vmcg
I've usually found that sort of thing's caused by windshear or to a lesser extent immediately after take-off, temperature inversion which tends to get you a little later (another good reason to achieve V2 +10)
Not regularly but at max RTOW it requires a bit of attention but then so do lightweight departures zooming (good tabloid term) up to/through initial cleared altitude.
The standard phrase for drawing other crewmembers attention to any of the foregoing is: "What the F V K K 's up wi' this thing!"