I hoped here on turkishclass we are Turkish natives and Turkish learners...and all friends

For any Moslem, calling someone "gavur" is a very risky act, even when that someone appears to be in open defiance of god.

"Takva" is a term to define a person´s "closeness" to God.  Kuran openly states that it is not possible nor allowed for ordinary mortals to judge anyone else´s takva and comment on it,  since the rights for such an evaluation is exclusively reserved for God only. Calling someone "Gavur"  may be construed as an attempt to grade that person´s takva, hence as an interference with God´s bussiness: Such interference, according to Islam, is a major sin.