here's a line I have used....and it never EVER fails.
When it comes time for the bill or check; and YOU know it's easier for you to pay, and it is no big deal...pick it up and say, succintly, innocently but to the point-
"I'll get this and if you don't let me, well then when it comes time for the sex, then I'll have to insist on abstinence."
I have had a sheepish grin and the check handed to me immediately. I have had their hand pulled away ASAP. I have had a huge LMAO; but I still paid. I have had an embarrased pause with nothing to say. I have had a "it's all yours." "whatever you say." "whatever makes you happy." "not a problem."
And all of the like---but not once have I ever had a man insist on paying after that. And using the right tone and inflection of voice it seems to come off without any intimidation factors. it just seems to take the male ego on money right off the table.