Committing evil actions by violating others' rights through killing, hitting, plundering, cursing or any thing like this is also meant here and whoever does so falls under this great danger. There is no doubt that disbelief is the greatest and most abominable of evil actions. Allah (Glorified be He) says:
And (remember) when Luqmân said to his son when he was advising him: "O my son! Join not in worship others with Allâh. Verily joining others in worship with Allâh is a great Zûlm (wrong) indeed.
May Allah grant us success, and peace and blessings be upon His Prophet and his family and Companiuons!