How to convince my mum to buy me boxers?

my Mum still buys all my underwear for me. Every year she buys me the awful packs of slips from cheap shops that she has been getting me since I was out if nappies. I just find it a bit awkward talking underwear with my mum so have avoided having the conversation about buying my own or asking her to buy boxers instead of slips.

Guys how did you start the conversation with your mum about changing from boys pants to boxer shorts or to buying your own underwear?
How to convince my mum to buy me boxers?
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