Everyone knows that we Muslims have a greeting of our own: السلام عليكم و رحمة الله و بركاته May the peace and mercy of Allah be upon you, as well His blessings. This greeting is actually a blessing from Allah, as He says in Surah Nur:
ا فَسَلِّمُوا عَلَىٰ أَنْفُسِكُمْ تَحِيَّةً مِنْ عِنْدِ اللَّهِ مُبَارَكَةً طَيِّبَةً ...then greet one another with a greeting from Allah, blessed and good. (24: 61)
When we meet a Muslim brother or sister, we should greet them using this greeting. We should wish peace upon them when meeting and when departing. The point is, when we say السلام عليكم, we mean to say that we have no bad feelings towards the person, or jealousy, or any other evil judgemental thoughts.
I ask Allah to give us the strength to greet every Muslim brother or sister whom we meet with the best greeting, and also the strength to replace our 'Hi's' with 'assalamu alaikum's'. :) Ameen.