What is ‘magbiru-biro’ in English?

You will use ‘around’

Merriam-Webster’s one usage of ‘around’: Used with some verbs to indicate repeated or continued action

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nagbibiru-biro

Lagi siyang nagbibiru-biro kung kailan dapat siya maging seryoso.

He is always joking around when he should be serious.

 

(always joking around when he should be serious — Merriam-Webster’s sample)

 

maglaru-laro

Huwag kang maglaru-laro ng iyong pagkain.

Don’t play around with your food.

 

(don’t play around with your food — Merriam-Webster’s sample)