Chat up lines and Valentine messages are separate things, surely?
Most women I know hate chat up lines anyway. They'd much prefer it if a guy went up to them with a smile, and introduced himself, and then asked if he could join them/buy them a drink, or simply ask or talk about the place they were at/in.
Valentine messages can just be funny or romantic, depending on the card and the person it's being given to.
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*****WARNING this link contains sexual swear words*****
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this song sums it up for me