The things I've regretted saying are usually when I've pointed out someone's ignorance and made them feel bad, when I should have smiled sweetly and said nothing. A guy once told me, "I've travelled all over the EU: Japan, China, Canada." Bloody moron.
I was never very good at talking to an idiot without letting him know he was one.

Oh that is bad, was he serious? are you sure he did not put an "and" after EU !!!!!
I have never uttered the "I love you" words to a client but some have said it to me and I hate it. Never know quite how to react and some of them have instantly regretted saying it to me obviously as what usually follow is "you know what I mean" or some such drivel.
One man came in and within one minute told me very loudly and clearly he would not be seeing me again. I just smiled. He then continued, saying he wanted to try a pro and then never do it again. How charming of him to let me know.

At the door with a really lovely regular client the other night I said without thinking "See you next week for the next instalment" I didn't mean what it sounded like, I meant to say 'our next encounter' 

Hehe Sometimes I tease Clients by saying; " yes, you already told me about that..I have it down in chapter 2 "  It's worth it for the look of terror on their face 

'you look like an elf, can't beleive i'm fucking an elf this is great'. (he clarified he meant like in a good way like elven features rather than a ginger short leprcaun or santas grotto worker) But during i was like...... OOohhh yea....... *wut..... eh whatever floats your boat, i've heard of weirder fantasies*

I guess this technically doesn't qualify as it was in an email but thoguht it worth a giggle.

Client called me Rhino instead of Rhona haha (I assume auto correct)  . Best misspelling of my workname yet. That'd make a very intimidating work name.

Hello sexy, my names RHINO.

Love it! My AW name is a bit ridiculous but I've never bothered to change it, I love hearing men awkwardly say it over the phone, it makes me howl.

Client called me Rhino instead of Rhona haha (I assume auto correct)  . Best misspelling of my workname yet. That'd make a very intimidating work name.

Hello sexy, my names RHINO.

I love this!

In a similar vein, my working name is Violet - I once had a client (who didn't speak a lot of English) mishear it as 'Violent'. Still makes me laugh whenever I think of it!