Calling a neutral official a cheat must be a red card, every single time. It attacks the integrity and the fair and independent arbitration of the match official; it's completely undermining the position and the authority. It's offensive.
What gets a little more difficult are comments like 'take off your yellow shirt' or other comments which are, arguably, implying bias. You might find more of a mixed opinion on here; though you'll probably find most people on here are in favour of a red for that.
Calling a player a cheat is different. Players, generally speaking, acknowledge that anything is fair game as long as it gets a win - a far cry from referees who work very, very hard at not only being fair, but being seen to be fair.
Every player who has taken a dive has cheated. I could argue that claiming a throw in when the player knows it came off him last is cheating.
I feel like these sorts of words warrant some intervention - it is quite rare for a player to call another a cheat and if that's happening, tempers are probably fraying - and the player saying it may well decide to take some retaliation on the player he thinks is cheating (usually it's an accusation of a dive).
But also focus on the manner. A player on the ground and an opponent standing over them yelling to 'get up you cheat!!' is aggressive, likely to incite a confrontation and usually warrants a yellow.
Though if I just happen to agree with the player and am intending to caution for a dive I might be inclined to let that player get away with the comment if it doesn't cause too much of an issue - I mean, heck, by issuing the card I'm clearly agreeing with him!
Now that I'm thinking back, this sort of comment more likely happens when the players are exchanging words from some distance, usually a 'that'll do lads, get on with the game!' is sufficient to shut them up.
Is it offensive, insulting or abusive? There's your answer
What does football expect??
Answers like these aren't the slightest bit helpful to new members. Answers like these are more likely to make new members wonder 'why should I bother with this forum?'
It's an education site. There's an old saying of there being no such thing as stupid questions, only stupid answers.
If somebody is asking what seems like a pretty basic question, help them out rather than respond with pointless, borderline troll posts. Not conducive to a helpful, supportive, education environment, is it?
No matter how black and white you may think it is, it's an interpretation of law question. A simple answer shouldn't have been too much to ask for.
Quite clearly the OP is asking 'what football expects' or if he should be considering these comments to be 'offensive, insulting or abusive'. So clearly comments like that aren't going to be the slightest bit helpful. Let's keep it helpful and constructive, hmm?