Context
Telling a friend their new haircut doesn't suit them.
Mira, te lo digo con todo el cariño del mundo, pero...
'I say this with all the love in the world, but...' — the standard Spanish setup for uncomfortable honesty.
British preamble to something that is slightly rude, contentious, or brutally honest — softens the blow just enough to say it anyway.
'No estoy siendo gracioso pero' sounds like you're worried people think you're joking. Doesn't land.
Context
Telling a friend their new haircut doesn't suit them.
Mira, te lo digo con todo el cariño del mundo, pero...
'I say this with all the love in the world, but...' — the standard Spanish setup for uncomfortable honesty.
Context
Pointing out that a colleague's plan won't work.
Oye, sin ánimo de ofender, pero...
'No offence intended, but...' — more formal but widely used.
Context
Saying something slightly controversial at a family dinner.
A ver, y esto que no salga de aquí, pero...
This stays between us, but... — adds conspiratorial flavour to the delivery.
Context
Telling a mate his girlfriend is trouble.
Te lo digo como amigo, ¿eh?
'I'm telling you as a friend' — the classic Spanish preamble before saying something they might not want to hear.
Context
Complaining about a situation at work.
No me malinterpretes, pero esto ya es demasiado.
Don't get me wrong, but this is too much — closer in structure to the English original.