MONTREAL, Canada - Sebastian Vettel says questioning his credentials as a four-times Formula 1 Drivers' champion is "disrespectful".After four consecutive successes, the most recent after an ultra-dominant second half of the 2013 season, the German has struggled to match new team mate Daniel Ricciardo so far in 2014 with a less competitive and unreliable car.Monaco, for example, was a particularly fraught weekend for Vettel, who was rarely confident his RB10 would keep running. He said in an interview published on May 4 2014 by German broadcaster RTL: "I've had many problems with the car so it's hard to get in a rhythm and get the best out of yourself."He said he was dealing with the "frustration" of 2014 by playing sports between races, taking out one of his road cars, or indulging his new passion, - motorcycling.'NOT FAIR'However in another interview, this one with German magazine Sport Bild, he blasted as "bullshit" any speculation his frustration might trigger a Red Bull exit. Also irking him is the suggestion 2014 was showing his true colours - not as "great" a driver in anything other than an ultra-dominant car.Vettel told RTL: "Looking back, I only had one race without problems. That was Malaysia. Again, I think it's just important to stay true to yourself - if the car is not working, you can be the best driver in the world, the victories will not come."I think if you want to make a comparison I remember when Michael (Schumacher) came back with Mercedes and the car was just not on the same level as him, maybe not at the level of his Ferrari, but there were many people who said '...Michael was just lucky when he won everything with Ferrari'. But, as I said, at some point you've already proved enough to yourself and to others."'BIT LIKE KINDERGARTEN'Indeed, Vettel hit back at critics who suggested he was not a worthy quadruple Drivers' champion, not on the level of some of F1's other multiple-title greats."Unfortunately in our day and age it is quite normal that you come to such judgements very quickly. I think you have to learn to deal with it. It's very easy to say something or write something - of course it's a pity and it's a bit like kindergarten but it's like that in F1. Everybody thinks everybody has something to hide."Asked if he thought suggestions that he had "forgotten how to drive" were disrespectful, Vettel answered: "That's the way the world is now. In a way it is disrespectful because these people do not know the background."Often they don't even want to know the background - they want to know how controversial and not-so-great it is, not how wonderfully everything is going."Stay with Wheels24 for the 2014 Canadian GP this weekend.