I won’t ask Colin for help because he is unreliable.
Frankly speaking, he is an unreliable man.
he’s lazy and unreliable
That car's so unreliable it'll never make it to London.
Do not count on him, he’s unreliable.
Moran has proven himself to be extremely unreliable.
It shows what an unreliable person he is.
He is a bit unreliable. (don't do what they say they will do).
He's a dishonest unreliable man so don't trust him
Jane is renowned for being unreliable, so expect her to be late.
He's totally unreliable as a source of information.
Emily cannot be trusted. She often cancels things at the last minute or just doesn't turn up. She is unreliable.
It’s such an unreliable bus service – I never know what time I'll arrive at the office!
unreliable witness, evidence
Our experiment has revealed that his report was unreliable.