What Irish expressions really mean this 

St.Patrick's Day 

May the Road Rise to Meet You - From the Gaelic, Go N-eiri an bothar leat, which means may success be with you.

Top of the Morning: Hollywood invention, never used in Ireland.
And the rest of the day to yourself - Also Hollywood.

Slainte: means Good health - Slainte is the Gaelic word for health.

Slan meaning farewell Slan is the Gaelic word for safe so it means keep safe.

Erin go Bragh - Means in Gaelic "Ireland forever."

A Hundred Thousand welcomes - from the Gaelic Cead Mile Failte which means literally that.

Dia is Muire Dhuit: Means hello in Gaelic, literally means "God and Mary with you."

Dia is Mhuire Duit agus Padraig; How the person responds,"God and Mary and St. Patrick with you."

Pog Mo Thoin - it means what you think it does, Gaelic for kiss my ...

And finally...
La Fheile Padraig brea dhibh go leir - Have a great St. Pat's everyone