Don't bother, summer's nearly over (well we do live in the UK), before you know it you'll be back to jeans and sweatpants, thus covering up thunder thighs. Added bonus, you can also stop shaving your legs then too.
Are they large because of fat or muscle ? If the latter then exercise may make them larger, although you could seek advice at the gym on trying to contour rather than grow them. If the former, and "flabby" suggests it is, well dieting doesn't get directed to the area you wish to reduce. Can only look at the whole of you and find the best weight compromise. Sometimes accepting yourself for who you are is the best course of action. Chunky legs look better than bony skeletal ones anyway.
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