That's the point. It's not about anything happening between OP's boyfriend and a tattooist.
The friend can't see a beautiful woman without supposing she'd give a blow job to any man within reach. (If you need further explanation, he's a misogynist and probably a sex pest.)
BF replies haha, I wish! Okay, that's a deflection. (We know men don't generally like to tell each other when they're being creeps. Shame, but there you go.)
Friend pushes it: You're lying, mate, I know you too well. Strong implication that friend thinks of BF as eager to get his dick sucked in any circumstances. (The friend probably thinks this is harmless banter, but he's now managed to insult BF as well as the tattooist.)
BF, incredibly, runs with this! He could've just said Don't be daft, or Speak for yourself, mate, or even Not these days, I'm going to be a father. He didn't. He just ran with this idea of both himself and the tattooist being sexually incontinent slags.
Even the friend seems surprised. He had to remind BF he's in a relationship.
Then BF says She's not here though. So - er, he's hoping the tattooist really will launch herself on his penis, since his girlfriend isn't there? She isn't there so anyone will do? There's NO POINT to this remark, except to highlight that his relationship status doesn't count unless his girlfriend is present. (Looks like the friend was on the money with I know you too well.)
I'd be fucking livid, OP.