There was one not too long ago, maybe 3 months. I really dont think RIOT likes that event because with a proper strategy which is letting enemy premades win every game in 6-7 minutes you earn up to 30 000 IP per day which is mindblowing and leaves RIOT with 2 options - either they ban everyone who abuses that and there are thousands of people who do and with that they lose their profit OR they let them do that and lose a ton of money because now you have 90 000 IP gathered over friday+weekend and you can buy so many champs without needing to buy RP for them. Its a lose lose for RIOT but I guess they will repeat it maybe 2 times a year. Expect more double IP weekends as they arent nearly as abusable.