For example, ...It's so true that my apology is too late but, believe it or not, I've been so burdened with the way to say sorry to you. I just felt uneasy to say that to you because it'd been too long to say even hello to you. My bad. I'm terribly sorry.."
In this case, does 'believe it or not' sound rude?
It's probably going to come off as rude. In modern usage, the phrase "believe it or not" often carries these meanings:
None of those connotations are going to be welcome in what's intended as an apology.
The phrase is also frequently used sarcastically, as in, "believe it or not, the world doesn't revolve around you." Again, in an apology, it's best to avoid phrases that could be easily misinterpreted as insults.
It doesn't appear to be necessary in your response. It sounds just fine if you were to omit the "believe it or not" part of your apology.
If I were to hear someone say that, it makes it sound like an excuse not to apologize and can come across as a rude statement.
Original:
"It's so true that my apology is too late but, believe it or not, I've been so burdened with the way to say sorry to you. I just felt uneasy to say that to you because it'd been too long to say even hello to you. My bad. I'm terribly sorry.."
You can try something like this:
"It's true that my apology is late, but I've been quite burdened with how to say I am sorry to you. I felt uneasy to say I'm sorry because it's been too long to even say hello to you. It's my fault and I'm terribly sorry."
I agree with the other answers that you really don’t need to (read: “shouldn’t) remind the person of his/her option/right to “believe [you] or not,” but if you really feel the need to include that notion, maybe the following version of it would come across as a bit less [yes, imo, rude and] “in-his/her-face,” (i.e., a bit less “take-it-or-leave-it”) (as for my other suggestions, you can, of course, “take them or leave them,” but they would provide a way for you to simultaneous say both of the things that you’ve apparently left unsaid for too long):
Although it's true that my apology is late, probably too late, as hard as it might be to believe, please know that I've been struggling to find a way to express my sincere regrets [for my behavior/words], just as I’ve been struggling [since then] to find the courage to simply tell you “Hello.”
I am now over these struggles:
Hello, it’s me, it’s all me and I'm so terribly sorry.
(S/he might get [and, if so, perhaps even appreciate] the Todd Rundgren reference in the actual apology suggested in the last sentence. Regardless I think “it’s me, it’s all me,” although still perhaps too informal, is, in my opinion, a more suitable way to say “It’s [all] my fault” than “My bad” in whatever apology you end up using.)
(“Hello, It’s Me” lyrics from ‘MetroLyrics’ and example usage of “It’s me, it’s all me” from ‘The Social Work Psychoanalyst's Casebook: Clinical Voices in Honor of Jean Sanville’ edited by Joyce Edward, Elaine Rose, via Google Books)
I would not say that it's rude. It does suggest that the relationship between the reader and the writer has had its ups and down, and can even be understood as the writer having previously supplied the reader with a number of excuses in the past.
I would drop the "my bad" part.
Here's an edited version:
My apology is late, but, believe it or not, I've been so burdened with how to say I'm sorry to you. I feel uneasy because it has been so long since I've said hello.
I'm terribly sorry.."
Well, I would never write " believe it or not". Why create doubt in mind of the reader. At the most say " believe me" or " to tell you the truth" And again say so if it is true. Falsity is a big no no for me.
Any phrase can sound rude, when used as a "trigger" to place the blame on the other party or to imply the other is at fault or untrustworthy. Or to deliberately sound insincere in your apology.
Are you done?
You still look and sound like you're 25.
Hello.
Believe or not.
