From this great site Fun Latin comes useful latin phrases for everyday life:

My dog ate it.
Canis meus id comedit.

I’m not interested in your dopey religious cult.
Nihil curo de ista tua stulta superstitione.

I am not lost.
Neutiquam erro.

Accidentally on purpose
Casu consulto

IF YOU CAN READ THIS BUMPER STICKER, YOU ARE BOTH VERY WELL EDUCATED AND MUCH TOO CLOSE
SIC HOC ADFIXUM IN OBICE LEGERE POTES, ET LIBERALITER EDUCATUS ET NIMIS PROPINQUUS ADES

Your fly is open.
Braccae tuae aperiuntur.

Go ahead. Make my day.
Age. Fac ut gaudeam.

… and last but not least, for all your romantic Wedding Skulls readers:

Have you lost weight?
Nonne macescis?

Your place or mine?
Apudne te vel me?

It looks great on you!
Id tibi praebet speciem lepidissimam!

Your slip is showing.
Subucula tua apparet.